Flexible capacity satellite communications system

ABSTRACT

Systems and methods for supporting more flexible coverage areas and spatial capacity assignments using satellite communications systems are disclosed. A hub-spoke, bent-pipe satellite communications system includes: terminals; gateways; a controller for specifying data for controlling satellite operations in accordance with a frame definition including timeslots for a frame and defining an allocation of capacity between forward and return traffic; and a satellite including: pathways; at least one LNA, an output of which is for coupling to a pathway and to amplify uplink beam signals in accordance with the allocation; and at least one HPA, an input of which is for coupling to the pathway and to amplify downlink beam signals in accordance with the allocation, and wherein the frame definition specifies at least one pathway as a forward pathway for at least one timeslot and as a return pathway for at least one other timeslot in the frame.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/666,112, filed on Nov. 1, 2012, and entitled “Flexible CapacitySatellite Communications System,” which is a continuation of PCTApplication No. PCT/US2011/034845, filed on May 2, 2011, and entitled“Flexible Capacity Satellite Communications System,” which claimspriority to U.S. patent application Ser. No. 13/098,334, filed on Apr.29, 2011, and entitled “Flexible Capacity Satellite CommunicationsSystem with Flexible Allocation Between Forward and Return Capacity,”and U.S. patent application Ser. No. 13/098,213, filed on Apr. 29, 2011,and entitled “Flexible Capacity Satellite Communications System withDynamic Capacity Distribution and Coverage Areas,” each of which claimsthe benefit of priority under 35 U.S.C. §119(e) of U.S. ProvisionalApplication Nos. 61/330,377, filed on May 2, 2010, and 61/375,384, filedon Aug. 20, 2010, both entitled “Flexible Capacity CommunicationSatellite System;” and the entireties of all of which are hereinincorporated by reference for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to satellite communicationssystems. More particularly, the present invention relates to methods andsystems for providing more flexible coverage areas and spatial capacityallocations using satellite communications systems.

BACKGROUND OF THE INVENTION

Legacy satellite communication systems have employed simple “bent-pipe”satellites that relay signals among terminals located in the same largeantenna footprint, for example, the continental Unites States. Due tothe overlap of transmit and receive coverage areas, separate frequencybands are used for the uplink (to the satellite) and the downlink (fromthe satellite). The “bent-pipe” designation refers to the fact that therelayed signals are effectively retransmitted after the signals arereceived by the satellite, as if redirected through a bent pipe. Thedata in the relayed signals is not demodulated or remodulated as in a“regenerative” or processing satellite architecture; signal manipulationon the satellite in a bent-pipe architecture is generally limited tofunctions such as frequency translation, filtering, amplification, andthe like.

Later satellite communication systems were developed around satellitesthat employ innovations such as digital channelization and routing ofsignals, demodulation/routing/re-modulation of the data in the relayedsignals, narrow antenna footprint “spot” beams to allow frequency reuse,and phased array antennas to allow dynamic placement of coverage areas.

For example, satellites for Mobile Satellite Services (MSS) typicallyemploy spot beam coverage areas with a high degree of frequency reuse.Examples of satellites for MSS include the Inmarsat-4 satellites and theThuraya satellites. These satellites typically feature a large number ofsmall spot beams covering a large composite area and allow for flexibleand configurable allocation of bandwidth. However, the total systembandwidth is very low (such as a 34 MHz allocation at L-band), andservice is generally categorized as “narrow band” (e.g., carrierbandwidths of hundreds of kHz), which allows the flexible andconfigurable bandwidth allocation to be done using digital beamformingtechniques. These satellites use a large reflector with an active feedarray. The signals from each feed element are digitized, and thebeamforming and bandwidth flexibility are provided by a digital signalprocessor. The digital beamforming is performed on narrowband channels,allowing any narrowband channel on the feeder link to be placed at anyfrequency for any spot (or other) beam shape.

The Wideband InterNetworking Engineering Test and DemonstrationSatellite (WINDS) is an experimental Ka-band satellite system. Thesatellite implements both fixed spot beams using a fixed multi-beamantenna (MBA) and an active phased array antenna (APAA). The MBA servesfixed beams, and the communications link can be switched over time in apattern consisting of combinations of receiving and transmitting beams.The APAA has been developed as a beam-hopping antenna with a potentialservice area that covers almost the entire visible region of earth fromthe satellite. The APAA can provision communications between arbitraryusers using two independently steerable beams for each of thetransmitting and receiving antennas. Beam steering is achieved byupdating pointing directions via control of digital phase shifters inswitching interval slots as short as 2 ms in Satellite Switched TimeDivision Multiple Access (SS-TDMA) mode, where the shortest beam dwelltime corresponds to the slot time of the SS-TDMA system. Beam switchingat high speed is supported for up to eight locations per beam. Switchingpatterns for both the MBA and APAA are uploaded from a networkmanagement center.

Spaceway is a Ka-band satellite system that services 112 uplink beamsand nearly 800 downlink beams over the United States. The Spacewaysatellite uses a regenerative on-board satellite processor to route datapackets from one of 112 uplink beams to one of nearly 800 possibledownlink beams. At any time the downlink consists of up to 24 hoppingbeams. The downlink scheduler determines which beams should betransmitting bursts for each downlink timeslot depending on each beamsdownlink traffic queue and power and interference constraints.

The Wideband Global SATCOM (WGS) satellite, formerly known as theWideband Gapfiller Satellite, is a U.S. government satellite thatemploys steerable Ka-band spot beams and X-band beamforming. The Ka-bandspot beams are mechanically steered. Up to eight X-band beams are formedby the transmit and receive X-band arrays using programmable amplitudeand phase adjustments applied to beamforming modules (BFMs) in eachantenna element. Bandwidth assignment is flexible and configurable usinga broadband digital channelizer, which is not involved in beamforming.

More recent satellite architectures have resulted in further dramaticincreases in system capacity. For example, ViaSat-1 and the Ka-band spotbeam satellite architectures disclosed in Dankberg et al. U.S. Pat. App.Pub. No. 2009-0298416, which is incorporated by reference herein in itsentirety, can provide over 150 Gbps of physical layer capacity. Thisspot beam architecture provides over an order of magnitude capacityincrease over prior Ka-band satellites. Other satellites, for exampleKA-SAT and Jupiter, use similar architectures to achieve similarly highcapacities. The architecture used in all of these satellites is a “bentpipe” hub-spoke architecture that includes small spot beams targeted atfixed locations. Each spot beam may use a large amount of spectrum,typically 250-1000 MHz. The resulting large capacity is a product ofseveral characteristics of the satellite system, including, for example,(a) the large number of spot beams, typically 60 to 80 or more, (b) thehigh antenna directivity associated with the spot beams (resulting in,for example, advantageous link budgets), and (c) the relatively largeamount of bandwidth used within each spot beam.

The aforementioned high capacity satellite architectures are extremelyvaluable, but may still be limited in certain respects. For example,scaling the architecture to support higher capacities while maintainingthe same spectrum allocation and power budget is typically accomplishedusing larger reflectors to create spot beams with smaller diameters. Theuse of smaller diameter spot beams may increase the directivity (orgain) of the satellite antenna, thus enhancing the link signal-to-noiseratio (SNR) and capacity. However, the smaller beams necessarily reducethe coverage area (e.g., the area for which satellite service can beprovided). These satellite architectures, therefore, have an inherenttradeoff of capacity versus coverage area.

In addition, these architectures typically place all spot beams, bothuser beams and gateway (GW) beams, in fixed locations. There isgenerally no ability to move the spot beams around to accommodatechanges in the coverage area. Moreover, the architectures essentiallyprovide uniformly distributed capacity over the coverage area. Thecapacity per spot beam, for example, is strongly related to theallocated bandwidth per spot beam, which is predetermined for every spotbeam and allows for little to no flexibility or configurability.

Although these high capacity architectures are extremely valuable whenthe desired coverage area is well-known and the demand for capacity isapproximately uniformly distributed over the coverage area, theinflexibility of the aforementioned architectures can be limiting forcertain applications. What is needed, therefore, is a satellite systemarchitecture that provides high capacity, large coverage areas,increased flexibility, for example, in the locations of the coverageareas and gateways and in the spatial distribution of the capacity, anability to change coverage areas, gateway locations, and capacityallocation during the lifetime of the satellite, and a flexible designthat could be useful in many orbit slots or allow moving the satelliteto another orbit slot during the mission lifetime.

SUMMARY OF THE INVENTION

In view of the foregoing, a more flexible satellite communicationssystem is provided. An example of a hub-spoke, bent-pipe satellitecommunications system includes: multiple terminals; multiple gatewaysconfigured to communicate with the multiple terminals; a controllerconfigured to specify data for controlling satellite operations inaccordance with a frame definition, the frame definition includingmultiple timeslots for a frame and defining an allocation of capacitybetween forward traffic, from at least one gateway to multipleterminals, and return traffic, from multiple terminals to at least onegateway; and a satellite including: multiple pathways; at least one lownoise amplifier (LNA), wherein an output of the at least one LNA isconfigured to be coupled to a pathway of the multiple pathways and toamplify uplink beam signals in accordance with the allocation ofcapacity between forward traffic and return traffic defined by the framedefinition; and at least one high power amplifier (HPA), wherein aninput of the at least one HPA is configured to be coupled to the pathwayof the multiple pathways and to amplify downlink beam signals inaccordance with the allocation of capacity between forward traffic andreturn traffic defined by the frame definition, and wherein the framedefinition specifies configuration of at least one pathway of themultiple pathways as a forward pathway for at least one timeslot in theframe, and configuration of the at least one pathway as a return pathwayfor at least one other timeslot in the frame.

Embodiments of such a satellite communications system may include one ormore of the following features. The satellite further includes one ormore beam forming networks configured to couple the output of the atleast one LNA to the pathway of the multiple pathways and to couple theinput of the at least one HPA to the pathway of the multiple pathways.The satellite further includes a phased array of antenna elements, andan input of the at least one LNA is configured to be coupled to anoutput of an antenna element of the phased array. The satellite furtherincludes a phased array of antenna elements, and at least one harmonicfilter, wherein an output of the at least one harmonic filter isconfigured to be coupled to an input of an antenna element of the phasedarray, and an output of the at least one HPA is configured to be coupledto an input of the at least one harmonic filter.

An example of a method for hub-spoke, bent-pipe satellite communicationutilizing a satellite containing multiple pathways and in communicationwith multiple terminals and multiple gateways, includes: at acontroller, specifying data for controlling satellite operations inaccordance with a frame definition, the frame definition includingmultiple timeslots for a frame and defining an allocation of capacitybetween forward traffic, from at least one gateway to multipleterminals, and return traffic, from multiple terminals to at least onegateway; and at the satellite, receiving uplink beam signals andtransmitting downlink beam signals in accordance with the allocation ofcapacity between forward traffic and return traffic defined by the framedefinition, and wherein the frame definition specifies configuration ofat least one pathway of the multiple pathways as a forward pathway forat least one timeslot in the frame, and configuration of the at leastone pathway as a return pathway for at least one other timeslot in theframe.

An example of a satellite for hub-spoke, bent-pipe satellitecommunication includes: multiple pathways; at least one low noiseamplifier (LNA), wherein an output of the at least one LNA is configuredto be coupled to a pathway of the multiple pathways and to amplifyuplink beam signals in accordance with an allocation of capacity betweenforward traffic, from at least one gateway to multiple terminals, andreturn traffic, from multiple terminals to at least one gateway, definedby a frame definition, the frame definition including multiple timeslotsfor a frame; and at least one high power amplifier (HPA), wherein aninput of the at least one HPA is configured to be coupled to the pathwayof the multiple pathways and to amplify downlink beam signals inaccordance with the allocation of capacity between forward traffic andreturn traffic defined by the frame definition, and wherein the framedefinition specifies configuration of at least one pathway of themultiple pathways as a forward pathway for at least one timeslot in theframe, and configuration of the at least one pathway as a return pathwayfor at least one other timeslot in the frame.

Embodiments of such a satellite may include one or more of the followingfeatures. The satellite further includes one or more beam formingnetworks configured to couple the output of the at least one LNA to thepathway of the multiple pathways and to couple the input of the at leastone HPA to the pathway of the multiple pathways. The satellite furtherincludes a phased array of antenna elements, wherein an input of the atleast one LNA is configured to be coupled to an output of an antennaelement of the phased array. The satellite further includes a phasedarray of antenna elements, and at least one harmonic filter, wherein anoutput of the at least one harmonic filter is configured to be coupledto an input of an antenna element of the phased array, and an output ofthe at least one HPA is configured to be coupled to an input of the atleast one harmonic filter.

An example of a method for hub-spoke, bent-pipe satellite communicationutilizing a satellite containing multiple pathways and in communicationwith multiple terminals and multiple gateways, where the method isperformed at the satellite, includes: receiving uplink beam signals; andtransmitting downlink beam signals, wherein receiving the uplink beamsignals and transmitting the downlink beam signals are in accordancewith an allocation of capacity between forward traffic, from at leastone gateway to multiple terminals, and return traffic, from multipleterminals to at least one gateway, defined by a frame definition, theframe definition including multiple timeslots for a frame, and whereinthe frame definition specifies configuration of at least one pathway ofthe multiple pathways as a forward pathway for at least one timeslot inthe frame, and configuration of the at least one pathway as a returnpathway for at least one other timeslot in the frame.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the following drawings. In theappended figures, similar components or features may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label with a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the samereference label irrespective of the second reference label.

FIG. 1 is a simplified diagram of an illustrative satellitecommunications system in which the systems and methods disclosed hereinmay be used in accordance with embodiments of the present invention;

FIGS. 2A-2E show illustrative user beam locations in accordance with anembodiment of the present invention;

FIG. 3 shows an illustrative beam hopping frame in accordance with anembodiment of the present invention;

FIG. 4 is a simplified block diagram of an illustrative satellite inaccordance with an embodiment of the present invention;

FIG. 5 is a simplified block diagram of an illustrative receive beamforming network in accordance with an embodiment of the presentinvention;

FIG. 6 is a functional block diagram of a transmit feed forming networkin accordance with an embodiment of the present invention;

FIG. 7 is a simplified block diagram of an illustrative beam weightprocessor in accordance with an embodiment of the present invention;

FIG. 8A shows a simplified subset of a timeslot pathway in accordancewith an embodiment of the present invention;

FIG. 8B shows an illustrative timeslot definition table in accordancewith an embodiment of the present invention;

FIG. 8C shows illustrative timeslot pathways according to the timeslotdefinition table of FIG. 8B in accordance with an embodiment of thepresent invention;

FIG. 9 shows an illustrative process for supporting satellitecommunication in accordance with an embodiment of the present invention;

FIG. 12A shows an illustrative synchronized timeslot allocation inaccordance with an embodiment of the present invention;

FIG. 12B shows an illustrative timeslot definition table andillustrative timeslot pathways in accordance with an embodiment of thepresent invention;

FIG. 13A shows an illustrative interleaved timeslot allocation inaccordance with an embodiment of the present invention;

FIG. 13B shows an illustrative timeslot definition table andillustrative timeslot pathways in accordance with an embodiment of thepresent invention;

FIG. 14A shows an illustrative interleaved timeslot allocation inaccordance with an embodiment of the present invention;

FIG. 14B shows an illustrative timeslot definition table andillustrative timeslot pathways in accordance with an embodiment of thepresent invention;

FIG. 15A shows an illustrative dedicated pathways allocation inaccordance with an embodiment of the present invention;

FIG. 15B shows an illustrative timeslot definition table andillustrative timeslot pathways in accordance with an embodiment of thepresent invention;

FIG. 15C shows an illustrative timeslot definition table in accordancewith an embodiment of the present invention;

FIG. 15D shows an illustrative timeslot definition table in accordancewith an embodiment of the present invention;

FIG. 15E shows illustrative timeslot pathways in accordance with anembodiment of the present invention;

FIG. 16A shows illustrative non-congruent forward and return linkcoverage areas in accordance with an embodiment of the presentinvention; and

FIG. 16B shows illustrative timeslot pathways in accordance with anembodiment of the present invention.

FIG. 17 shows an illustrative chart of the number of gateways requiredversus the number of forward pathways allocated in accordance with anembodiment of the present invention.

FIG. 18A shows an illustrative beam hop pattern of a single beam for thetimeslot dwell times of a beam hopping frame in accordance with anembodiment of the present invention.

FIG. 18B shows an illustrative timeslot dwell time table in accordancewith an embodiment of the present invention.

FIG. 18C shows an illustrative beam hopping frame in accordance with anembodiment of the present invention.

FIG. 19A shows illustrative gateway locations and user beam locations inaccordance with an embodiment of the present invention.

FIG. 19B shows an illustrative gateway table in accordance with anembodiment of the present invention.

FIG. 19C shows illustrative placements of gateway locations inaccordance with an embodiment of the present invention.

FIG. 20 is a simplified diagram of an illustrative satellitecommunications system in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a more flexible high-capacity satellitecommunications architecture. Phased arrays are used to target spot beamson desired coverage areas across a given system coverage geography(e.g., high population areas in North America). The spot beams (orpathways) may then quickly hop from location to location according toweight vectors of a weight set and beam hop timeslot definitionsincluded in a beam hopping frame definition. The beam hopping timeslotdefinitions include associated dwell times and pathway gains for allbeams during one timeslot. The beam hopping timeslot definitionsincluded within a beam hopping frame definition may be automaticallyrepeated until a new beam hopping frame definition is received or aninterrupt is signaled, allowing for dynamic changes to the transmit andreceive coverage area and beam locations.

FIG. 1 is a simplified diagram of an exemplary satellite communicationssystem 100 in which the systems and methods disclosed herein may beimplemented. Satellite communications system 100 includes a network 120interfaced with one or more gateway (GW) terminals 115. Gateway terminal115 is configured to communicate with one or more user terminals 130 viasatellite 105. As used herein, the term “communicate” refers to eithertransmitting or receiving (i.e., unidirectional communication) whenapplied to a given pathway for a given polarization at a given instantof time.

Gateway terminal 115 is sometimes referred to herein as a hub or groundstation. Gateway terminal 115 services uplink 135 and downlink 140 toand from satellite 105. Gateway terminal 115 may also schedule trafficto user terminals 130. Alternatively, the scheduling may be performed inother parts of satellite communications system 100 (e.g., at one or morenetwork operations centers (NOC) and/or gateway command centers (notshown)). Although only one gateway terminal 115 is shown in FIG. 1 toavoid over-complication of the drawing, embodiments of the presentinvention may be implemented in satellite communications systems havinga plurality of gateway terminals each of which may be coupled to eachother and/or one or more networks.

In some satellite communications systems, there may be a limited amountof frequency spectrum available for transmission. Communication linksbetween gateway terminal 115 and satellite 105 may use the same,overlapping, or different frequencies as communication links betweensatellite 105 and user terminals 130. Gateway terminal 115 may also belocated remote from user terminals 130 to enable frequency re-use.

Network 120 may be any type of network and can include, for example, theInternet, an IP network, an intranet, a wide-area network (WAN), alocal-area network (LAN), a virtual private network (VPN), a virtual LAN(VLAN), a fiber optic network, a hybrid fiber-coax network, a cablenetwork, a public switched telephone network (PSTN), a public switcheddata network (PSDN), a public land mobile network, and/or any other typeof network supporting communications between devices as describedherein. Network 120 may include both wired and wireless connections aswell as optical links. Network 120 may connect gateway terminal 115 withother gateway terminals that may be in communication with satellite 105or with other satellites.

Gateway terminal 115 may provide an interface between network 120 andsatellite 105. Gateway terminal 115 may be configured to receive dataand information directed to one or more user terminals 130. Gatewayterminal 115 may format the data and information for delivery torespective user terminals 130. Similarly, gateway terminal 115 may beconfigured to receive signals from satellite 105 (e.g., from one or moreuser terminals 130) directed to a destination accessible via network120. Gateway terminal 115 may also format the received signals fortransmission on network 120.

Gateway terminal 115 may use antenna 110 to transmit forward uplinksignal 135 to satellite 105. In one embodiment, antenna 110 may comprisea parabolic reflector with high directivity in the direction ofsatellite 105 and low directivity in other directions. Antenna 110 maycomprise a variety of alternative configurations and include operatingfeatures such as high isolation between orthogonal polarizations, highefficiency in the operational frequency bands, low noise, and the like.

Satellite 105 may be a geostationary satellite that is configured toreceive forward uplink signals 135 from the location of antenna 110.Satellite 105 may use, for example, a reflector, a phased array antenna,an antenna, or any other mechanism known in the art for reception ofsuch signals. Satellite 105 may receive the signals 135 from gatewayterminal 115 and forward corresponding downlink signals 150 to one ormore of user terminals 130. The signals may be passed through a transmitreflector antenna (e.g., a phased array antenna) to form thetransmission radiation pattern (e.g., a spot beam). Satellite 105 mayoperate in a multiple spot-beam mode, transmitting a number of narrowbeams directed at a different region of the earth. This may allow forsegregation of user terminals 130 into the various narrow beams.

Satellite 105 may be configured as a “bent pipe” satellite. In thisconfiguration, satellite 105 may perform frequency and polarizationconversion of the received carrier signals before re-transmission of thesignals to their destination. A spot beam may use a single carrier,i.e., one frequency, or a contiguous frequency range per beam. A varietyof physical layer transmission modulation and coding techniques may beused by satellite 105 (e.g., adaptive coding and modulation).

Satellite communications system 100 may use a number of networkarchitectures consisting of space and ground segments. The space segmentmay include one or more satellites while the ground segment may includeone or more user terminals, gateway terminals, network operationscenters (NOCs), and satellite and gateway terminal command centers. Theterminals may be connected via a mesh network, a star network, or thelike as would be evident to those skilled in the art.

Forward downlink signals 150 may be transmitted from satellite 105 toone or more user terminals 130. User terminals 130 may receive downlinksignals 150 using antenna 127. In one embodiment, antenna 127 and userterminal 130 together comprise a very small aperture terminal (VSAT),with antenna 127 measuring approximately 0.6 meters in diameter andhaving approximately 2 watts of power. In other embodiments, a varietyof other types of antennas 127 may be used at user terminals 130 toreceive downlink signals 150 from satellite 105. Each of user terminals130 may comprise a single user terminal or, alternatively, may comprisea hub or router (not shown) that is coupled to multiple user terminals.Each user terminal 130 may be connected to various consumer premisesequipment (CPE) comprising, for example, computers, local area networks,internet appliances, wireless networks, and the like.

In some embodiments, a Multi-Frequency Time-Division Multiple Access(MF-TDMA) scheme is used for upstream links 140 and 145, allowingefficient streaming of traffic while maintaining flexibility inallocating capacity among each of user terminals 130. In theseembodiments, a number of frequency channels are allocated which may befixed, or which may be allocated in a more dynamic fashion. A TimeDivision Multiple Access (TDMA) scheme may also employed in eachfrequency channel. In this scheme, each frequency channel may be dividedinto several timeslots that can be assigned to a connection (i.e., auser terminal 130). In other embodiments, one or more of the upstreamlinks 140, 145 may be configured using other schemes, such as FrequencyDivision Multiple Access (FDMA), Orthogonal Frequency Division MultipleAccess (OFDMA), Code Division Multiple Access (CDMA), or any number ofhybrid or other schemes known in the art.

User terminal 130 may transmit data and information to a network 120destination via satellite 105. User terminal 130 may transmit thesignals via upstream uplink 145 to satellite 105 using the antenna 127.User terminal 130 may transmit the signals according to a variety ofphysical layer transmission modulation and coding techniques, including,for example, those defined with the DVB-S2, WiMAX, LTE, and DOCSISstandards. In various embodiments, the physical layer techniques may bethe same for each of the links 135, 140, 145, 150, or may be different.

Satellite 105 may support a non-processed, bent pipe architecture withphased array antennas (e.g., phased array antennas) used to produce thesmall spot beams. The satellite 105 contains K generic pathways, each ofwhich can be allocated as a forward pathway or a return pathway at anyinstant of time. Large reflectors may be illuminated by a phased arrayproviding the ability to make arbitrary beam patterns within theconstraints set by the size of the reflector and the number andplacement of the antenna elements. Phased array fed reflectors may beemployed for both receiving uplink signals 135, 145, or both, andtransmitting downlink signals 140, 150, or both. The beam formingnetworks (BFN's) associated with the receive (Rx) and transmit (Tx)phased arrays may be dynamic, allowing for quick movement of thelocations of both the Tx and Rx beams. The dynamic BFN's may be used toquickly hop both the Tx and Rx beam positions. The BFN may dwell in onebeam hopping pattern (e.g., both Tx and Rx beams) for a period of timecalled a timeslot dwell time. Individual timeslots may all be associatedwith the same dwell time or different dwell times. A number Q of thesetimeslots, with each timeslot associated with a potentially differentreceive and transmit beam location pattern, are arranged into a sequencecalled a beam hopping frame. These frames can repeat, but may also bedynamic and time-varying. The duration and location of the receive andtransmit beams associated with beam hop timeslots can also vary, bothbetween frames and within a frame.

An example of user beam locations is shown in FIGS. 2A-2E. In thisexample, the allocated spectrum is W Hz, and two polarizations (e.g.,LHP and RHP) are available. At any instant of time, 40 user beams may beactive, 20 LHP and 20 RHP, although more or fewer beams may be active inactual implementations. Each user beam may use the full W Hz ofallocated spectrum, but only one polarization. In other embodiments,each user beam may use only a portion of the allocated spectrum. In thedescribed example, a frame consists of Q=4 timeslots, although actualimplementations may use frames with more or fewer timeslots. During eachtimeslot, the user receive and transmit beams may reside at differentlocations. The hopping pattern may automatically repeat at theconclusion of each frame or a new frame definition may be applied tovary the hopping pattern. For example, FIG. 2A includes beam map 200showing exemplary beam locations during the first timeslot of the frame.A beam labeled with an “L” in the center indicates a LHP beam and a beamlabeled with an “R” indicates a RHP beam, although any number of otherpolarizations may be used in other embodiments. Due to the small beamdiameters, desired large spread of the coverage area, and the relativelysmall number of beams active at one time, beams that use the samepolarization during a given timeslot may be spaced relatively far apart.This may lead to low interference levels between the beams. Theresulting high carrier to interference ratio (C/I) may help to increasethe capacity per beam. FIG. 2B includes beam map 210 showing exemplarybeam locations during the second timeslot of the frame. FIG. 2C includesbeam map 220 showing exemplary beam locations during the third timeslotof the frame. FIG. 2D includes beam map 230 showing exemplary beamlocations during the fourth timeslot of the frame. As described in moredetail below, each beam shown in FIGS. 2A-2D may be part of a dedicatedreceive pathway, a dedicated transmit pathway, or a hybridtransmit/receive pathway.

In each of the beam maps shown in FIGS. 2A-2D, beams of the samepolarization are generally spaced very far apart (e.g., at the maximumdistance possible). This spacing enables large values of C/I byminimizing interference from other active beams of the samepolarization. The selection of the actual locations for the beams maydepend on such factors as the desired system coverage area, the coveragediameter of each beam, the number of polarizations used, and the numberof timeslots per frame. FIGS. 2A-2D provide just one example. Finally,FIG. 2E includes coverage map 240 showing a composite overlay of all thebeams during all four timeslots (e.g., the system coverage area). Onlybeams of the same timeslot in FIG. 2E are active at the same time. Onlybeams of the same timeslot and the same polarization (e.g., LHP or RHP)present the potential for significant interference. As mentioned above,the location of these beams should be selected so as to maximize theirspatial separation. Several geometric models may be used to maximize theseparation of beams of like polarizations.

FIG. 3 shows illustrative beam hopping frame 300 with Q=16 timeslots perframe. In the depicted example, each timeslot occupies a 1.5 mSecinterval resulting in a total beam hopping frame duration of 24 mSec. Abeam, therefore, may be active in a given area for a minimum of 1.5 mSecor 1 timeslot, although a beam may be active in the same cell for morethan 1 consecutive timeslot depending on the timeslot definitionsincluded in the beam hop frame definition. In some embodiments, a singleregion within the composite coverage area, denoted a cell, might onlyhave one active beam on the region for one timeslot in the beam hoppingframe. The length of the beam hopping frame, therefore, may representthe potential waiting duration before information can be transmitted orreceived. It may be desirable to use this architecture for low latencyapplications, such as voice, so this hopping frame delay should be madeinsignificant relative to other unavoidable delays. For example, for asatellite in a Geo-Synchronous Orbit (GSO), the one-way path delay isapproximately 250 mSec and is an unavoidable delay. Therefore, selectionof a beam hopping frame length approximately 1/10 this value or lessrenders the framing delay insignificant relative to the unavoidableone-way path delay. Thus for a GSO satellite a frame size on the orderof 25 mSec is generally adequate. Shorter frame sizes may notsignificantly change the total delay experienced, as it is dominated bythe one-way path delay, and will generally result in more overhead andincreased complexity due to the fact that the beams are hopping faster.Thus, a beam hopping frame size of approximately 25 mSec is suitable formost applications.

In other embodiments, more than one beam may be active in a cell duringa single frame. For example, regions or cells may be assigned prioritiesindicative of the maximum acceptable delay for supported applicationswith the region or cell. Assigned priorities may then be used, at leastin part, to determine the number of active beams in a particular regionor cell per frame. For example, to support higher bandwidth or lowerlatency applications within a region or cell, the region or cell may beassigned a higher priority than a region or cell supporting lowerbandwidth or higher latency applications. Cells or regions assignedhigher priorities may have more than one active beam covering that cellor region in a single frame. Any number of priorities may be definedcorresponding to any number of active beams for an individual cell perframe. A single cell may have a maximum of Q transmit beams and Qreceive beams active in that cell in a single frame (e.g., beams areactive in the cell during all timeslots). In some embodiments, atransmit beam and a receive beam may be active in the same cell duringthe same timeslot, allowing for both transmission and reception of datain the same timeslot.

Satellite Payload Block Diagram

FIG. 4 shows a block diagram for part of exemplary satellitearchitecture 400 built in accordance with the present invention. Antennaelements 402 and 404 are shown for both LHP and RHP to support multiplepolarizations. In some embodiments (not shown), the satellitearchitecture supports only a single polarization. In other embodiments,the satellite architecture operates with a single polarization althoughit supports multiple polarizations. Two separate antenna systems areused in the example of FIG. 4, one for Rx and one for Tx, but anintegrated Tx/Rx antenna system could also be used. Each antenna systemmay include large reflector 406, 408 which is illuminated by a phasedarray consisting of L antenna elements in the array. The example of FIG.4 uses a phased array fed reflector as its antenna system, but DirectRadiating Array (DRA) or any other type of phased array based antennasystem that uses a beam forming network may be used in otherembodiments. The Rx system may consist of L_(rx) elements in the phasedarray, the output of each element port may be connected to a Low NoiseAmplifier, LNA. Each LNA may be located close to the associated feedelement to minimize the system noise temperature. Ideally, the LNA's maybe attached directly to the feed elements, which will yield an optimalnoise figure. The output of each of the 2×L_(rx) LNA's is routed to Rxbeam forming network 410, which is composed of both LHP and RHPsections. Since the system noise figure is essentially set by the LNA's,Rx beam forming network 410 can be located away from the LNA's with aninterconnection of, for example, coaxial cable or a waveguide. Rx beamforming network 410 may take the 2×L_(rx) inputs and provide K outputsignals, each corresponding to one of the K Rx beams. Rx beam formingnetwork 410 may operate at the Rx frequency and provide no frequencytranslation, in this example.

The K outputs of Rx beam forming network 410 from both the LHP and RHPsections may be fed through K signal pathway hardware sections. In someembodiments, the same number of pathways are used for each availablepolarization (e.g., LHP and RHP), although in general there may be adifferent number of pathways connected to the received signals of eachpolarization. Each pathway of the bent-pipe architecture typicallyconsists of a frequency conversion process, filtering, and selectablegain amplification. Other forms of processing (e.g., demodulation,remodulation, or remaking of the received signals, like in a“regenerative” system) are not performed when using a bent-pipearchitecture. The frequency conversion may be required to convert thebeam signal at the uplink frequency to a separate downlink frequency,for example, in a bent-pipe architecture. The filtering generallyconsists of pre-filtering before the downconverter and post-filteringafter the downconverter and is present to set the bandwidth of thesignal to be transmitted as well as to eliminate undesired mixerintermodulation products. The selectable gain channel amplifier mayprovides independent gain settings for each of the K pathways in theexample of FIG. 4.

Tx beam forming network 412, which may include both LHP and RHPsections, may generate 2×L_(rx) outputs from the K pathway outputsignals. In some embodiments, the pathway output signals that derivefrom an LHP receive beam may be output on a RHP transmit beam, and viceversa. In other embodiments, the pathway output signals that derive froman LHP receive beam may be output on a LHP transmit beam. Tx beamforming network 412 may operate at the Tx frequency and may provide nofrequency translation in this example. The outputs of Tx beam formingnetwork 412 are routed to 2×L_(tx) high power amplifiers (HPA's). Theharmonic filters (HF) connected to the output of each HPA may performlow pass filtering to provide suppression of the 2^(nd) and higher orderharmonics, for example, from the output of the HPA's. The output of theharmonic filters may then be input to the 2×L_(tx) feed elements in theTx phased array. Each HPA and harmonic filter may be located close tothe associated Tx feed element to minimize the losses. Ideally, theHPA/HFs may be attached directly to the Tx feed elements, which mayyield an optimal radiated power.

As shown in FIG. 4, separate reflectors 406, 408 and feed arrays may beused for the Tx and Rx beams. However, as described above, in someembodiments a single reflector and a single feed array are used toperform both Tx and Rx functions. In these embodiments, each feed mayinclude two ports, one for Tx and one for Rx. For a system using twopolarizations (e.g., RHP and LHP), a 4-port feed (2 for Tx and 2 for Rx)may be included. To maintain acceptable Tx to Rx isolation, such asingle reflector approach may also employ diplexors or other filteringelements within some or all of the feed elements. These filteringelements may pass the Rx band while providing suppression in the Txband. The increased number of feed elements and the phase matchingrequirements for the BFN's can make this approach more complex toimplement but may reduce costs associated with multiple reflectors andmultiple feed arrays.

In some embodiments, Rx beam forming network 410, Tx beam formingnetwork 412, or both, may use time-varying beam weights to hop receivebeams location, transmit beam locations, or both, around over time.These beam weight values may be stored in Beam Weight Processor (BWP)414. BWP 414 may also provide the control logic to generate the properbeam weights at the proper times. BWP 414 may be connected to the groundvia bi-directional data link 416, which can be in-band with the trafficdata or out-of-band with its own antenna and transceiver. Bi-directionaldata link 416 is shown as bi-directional in the example of FIG. 4 toassure that the correct beam weights have been received by BWP 414. Assuch, error detection and/or correction techniques, includingretransmission requests, may be supported using the bi-directional link.In other embodiments, a uni-directional link is used with errordetection and/or correction. In some embodiments, an initial set of beamweights can be loaded into the memory of BWP 414 before launch.

Data link 416 may be used, for example, to receive pre-computed beamweights and deliver such weights to BWP 414. In some embodiments, thebeam weights are generated on the ground at a network management entitysuch as a Network Operational Center (NOC). The desired locations ofeach of the K Tx and Rx beams, along with the feed element radiationpatterns, may be used to generate the beam weight values. There areseveral techniques for generating appropriate beam weights given thedesired beam locations. For example, in one approach, beam weights maybe generated on the ground in non-real time. The dynamic weights maythen be uploaded to BWP 414 through data link 416, and then applied tothe BFN's in a dynamic manner to produce hopping beams on both the Rxuplink and the Tx downlink.

The downlink portion of data link 416 may be used to report the statusof the BFN's and to provide confirmation of correct reception of theuplinked beam weights. Correct reception of the beam weights can bedetermined by use of a traditional CRC code, for example. In the eventof incorrect reception, as indicated by a failure of the CRC to check,for example, the uplink transmission of the beam weights (or the portionof the beam weights that was deemed incorrect or invalid), may beretransmitted. In some embodiments, this process may be controlled by anautomatic repeat request ARQ retransmission protocol (such as, forexample, selective repeat ARQ, stop-and-wait ARQ, or go-back-N ARQ, orany other suitable retransmission, error detection, or error correctionprotocol) between the ground station and BWP 414.

In general, satellite architecture 400 provides for K generic hoppingpathways. Each pathway functionally consists of an Rx beam and a Txbeam, connected together through electronics and circuitry that providesignal conditioning, such as one or more of filtering, frequencyconversion, amplification, and the like. The pathways may each berepresented as bent pipe transponders that can be used in a hub-spokeconfiguration or a mesh configuration. For example, in one embodimentwith a mesh configuration, a pathway carries signals between a firstplurality of terminals and a second plurality of terminals via thesatellite. In accordance with the systems and methods described herein,the termination points (e.g., the Tx beam location and Rx beam location)for each pathway may be dynamic and programmable, resulting in a highlyflexible satellite communications architecture.

Receive Beam Forming Network

FIG. 5 shows example block diagram 500 of one polarization of a receivebeam forming network. The network may take in signals from L_(rx) feedelements and provides the signals of K_(p) LHP and RHP formed beams asoutputs. In this example, there are K_(p)=K/2 LHP receive beams and K/2RHP receive beams although different numbers of receive beams of eachpolarization may be used in other embodiments. Each input signal from afeed element is first split, via splitters 502, into K identical copies,one for each beam. Then K_(p) parallel beam formers are realized. Eachbeam former may include, among other components, amplitude and phaseadjustment circuitry 504 and summer 506. Each instance of amplitude andphase adjustment circuitry 504 may take an input signal from one of theL_(rx) splitters and provide an amplitude and phase adjustment to thesignal. The L_(rx) amplitude and phase adjusted signals may then besummed using summer 506 to produce the signal from one formed beam. EachRx beam output may then be fed into one of K_(p) independent signalpathways as discussed previously. The coefficients used to create thereceive beam of pathway 1 of the satellite are shown by dashed line 508in FIG. 5.

The process of adjusting the amplitude and phase of the signal may bemathematically described as the multiplication of the complex base bandrepresentation of the signal by a complex number (e.g., a complexweight). Letting the complex number be represented as w=I +jQ, themagnitude of w is the amplitude adjustment and the phase of w is thephase adjustment. In practice the amplitude and phase adjustment can berealized in a number of ways. Two common techniques in phased arrayantennas are vector multiplier circuits that take as an input the I andQ values, and circuits that have independent phase and amplitudeadjustment mechanisms and take as input the desired amplitude and phaseadjustments. One should recognize I+jQ as the rectangular coordinates ofthe complex number, w, and Amplitude/Phase as the polar coordinates ofthe complex number, w. The BFN may provide dynamic (changing) andprogrammable complex weight values on each of the K beam formers in bothhalves of the BFN. In practice, the BFN may generally have amplificationstages within the BFN structure to account for some or all of theinsertion losses of the devices used to perform the BFN functions (e.g.,splitting, weighting, and combining).

Transmit Beam (Feed) Forming Network

FIG. 6 shows functional block diagram 600 of one polarization of atransmit feed forming network (FFN). The network takes in signals fromK_(p) signal pathways (e.g., K/2 LHP and K/2 RHP pathways) and providesthe signals to each of the L_(tx) feed elements. Each input signal froma pathway is first split, via splitters 602, into L_(tx) identicalcopies, one for each feed element. Then L_(tx) parallel “feed formers”are realized. Each feed former may include amplitude and phaseadjustment circuitry 604 and summer 606. Amplitude and phase adjustmentcircuitry 604 may take an input signal from one of the K_(p) splittersand provides an amplitude and phase adjustment. The L_(tx) amplitude andphase adjusted signals are then summed using summer 606 to produce thesignal for transmission in one feed.

The process of adjusting the amplitude and phase of the signal may bemathematically described as multiplication of the complex base bandrepresentation of the signal by a complex number (e.g., a complexweight). Letting the complex number be represented as w=I+jQ, themagnitude of w is the amplitude adjustment and the phase of w is thephase adjustment. In practice, the amplitude and phase adjustment can berealized a number of ways (as described above with regard to FIG. 5).The first and last coefficients used to form the transmit beam ofpathway 1 of the satellite are shown by dashed line 608. The remainingcoefficients are not explicitly shown in the example of FIG. 6.

As described above with regard to the receive beam forming network, theFFN may provide dynamic (changing) and programmable complex weightvalues on each of the K feed formers in the FFN. In practice, the FFNwill also have amplification stages within the FFN structure to make upfor some or all of the insertion losses of the devices used to performthe FFN functions (e.g., splitting, weighting, and combining).

Beam Weight Processor

FIG. 7 shows example block diagram 700 of a Beam Weight Processor (BWP).Single or multiple board computer 702 (or equivalent) may be used tointerface with a bi-directional data link (e.g., data link 416 (FIG. 4))to a control station, which is typically a ground control station suchas a NOC. Generally, the NOC is different than the Telemetry, Tracking,and Control (TT&C) station, but it may be implemented in the TT&C ifdesired. The beam weights may be received for all the beams and alltimeslots. Computer 702, which may include one or more processorscoupled to memory, may implement an ARQ protocol providing feedback datato the data link transmitter for transmission down to the controlstation. The feedback data may include a notification of successful orunsuccessful reception of the uplink data. Uplink data may include, forexample, beam weights, dwell times, pathway gains, commands, and anyother suitable data.

The BWP or affiliated hardware may provide the bulk storage for aplurality of weight matrices. A weight matrix may include the set of allweight vectors used for transmission and reception of all beams in onetimeslot. A weight vector may include the group of L_(tx) or L_(rx)individual complex weights used to create one beam during one timeslot.Thus, a transmit weight vector includes individual complex transmitweights, while a receive weight vector includes individual complexreceive weights. Weight matrices are generally computed at the controlstation based on the desired beam locations (e.g., the desired locationsof the transmit beams, the receive beams, or both) for each timeslot inthe beam hop frame. A beam hop frame may include a sequence of beam hoptimeslots, each timeslot with an associated dwell time. The dwell timemay be fixed for all slots, or the dwell time can be variable on atimeslot by timeslot basis, with the dwell times potentially changingframe by frame. In one example, a dwell time can be the duration of avariable number of timeslots, where each timeslot is of fixed duration.In another example, a dwell time can be the duration of one or moretimeslots, where the durations of the timeslots vary.

In some embodiments, a weight set includes the set of all weight vectorsused for transmission and reception of all beams in all timeslots of abeam hopping frame. Additionally or alternatively, a beam hop framedefinition may include a linked list of beam hop timeslots. In thelinked list approach, a dynamic dwell time for each timeslot may beeasily incorporated into the linked list. Any other suitable datastructure may also be used for frame definitions. The beam hop framedefinition can also include pathway gains for setting a selectable gainchannel amplifier for each pathway, for example, as illustrated in FIG.4.

In an example satellite using the beam weight set approach, a smallnumber (e.g., tens) of weight sets can be pre-computed and uploaded tothe BWP in the satellite. These weight sets can then be switched intooperation at any time via a single command from the ground indicatingwhich weight set to use and at what time. This allows switching weightsets without requiring a significant amount of information to beuploaded to the BWP. For example, in some embodiments, 24 completeweight sets are pre-computed, uploaded, and stored in the BWP computer.Once an hour (or on any other suitable schedule), a different weight setmay be selected for use by the BWP via the data link. This allows thecoverage and capacity allocation to track, for example, the hourlyvariations of the demand on a daily or 24-hour basis.

A beam weight set may include a significant amount of data. For example,in some embodiments, a weight set may include data corresponding toL_(tx)+L_(rx) feed elements (e.g., 1024)×K pathways (e.g., 80)×Qtimeslots (e.g., 64)×the number of bits required per weight (e.g., 12, 6bits for I and 6 bits for Q). For example, in FIG. 7, this sums toapproximately 16 MB of data per weight set. Data and command uplink tothe satellite may typically not be very fast. Even at a 1 Mbps datalink, it would take 128 seconds to upload the 16 MB weight set. Thus,pre-loading many weight sets in non-real time may be more convenient forcertain applications.

One of the stored weight sets in the BWP may be selected as the activeweight set and used in the generation of the hopped beams. This activeweight set may be stored in memory 704, such as a dual port RAM, thatallows computer 702 to load the next active weight set and some externallogic to dynamically access the individual weight vectors of the currentactive weight set. The individual weight vectors of the active weightset may then be output as beam weights at the proper time under controlof sequential logic 706. An example of sequential logic 706 may includetimeslot counter 708 that is incremented once per timeslot. Timeslotcounter 708 may be a simple 6-bit counter in some embodiments and mayhandle frames with up to 2⁶=64 timeslots per frame. The counter valuemay represent the slot number (e.g., 1 . . . 64) of the beam hoppingframe. Sequential logic 706 takes the output of timeslot counter 708 andmay generate (1) the proper addresses for memory 704, (2) addresses forthe latches in the BFN modules, and (3) the control signals to place thebeam weights on the data bus. Sequential logic 706 may then load thisdata into the appropriate latches in beam forming modules 710.

Within beam forming modules 710, data may be double latched to allow allof the beam weights within each weight vector to change at the sametime. This may ensure hopping of all beams synchronously with thetimeslot boundary. The data may be loaded into the first latch based onenable signals, which are decoded from the latch address by decoder 712.Then all data may be simultaneously loaded into the digital-to-analog(D/A) converters synchronously with a strobe signal from the sequentiallogic. The strobe may be generated within sequential logic 706 to occurat the start of each timeslot.

In the example of FIG. 7, certain components are shown within the BFNmodules. This approach may be advantageous since it may reduce orminimize the number of connections between the BWP and the BFN modules,but other possible implementations may be used. For example, theinterconnect signals may be limited to the 48-bit data bus, the latchaddress bus, plus a strobe line. The 48-bit data bus may enable loadingof 4 complex weights at one time (based on 6 bits for I+6 bits for Q×4weights=48 bits). In this example, there is a total of L=1024 feedelements×K=80 pathways×2 (for Tx and Rx), for a total of 163,840 complexweights. Loading 4 complex weights at a time requires 40,960 addressablelocations, or a 16-bit latch address bus resulting in a totalinterconnect of 48+16+1=65 lines.

In some embodiments, the address decoding, latches, and D/A's areincorporated in the BWP itself. This may simplify the BFN modules, butsignificantly increase the required number of interconnects. Forexample, using L=1024 elements×K=80 pathways×2 (for Tx and Rx)×2 (I andQ)=327,680 analog voltage (D/A output) lines.

Example Satellite and Pathways

FIG. 8A shows subset 800 of the payload of a K=4 pathways satellite. Theinstantaneous (e.g., timeslot) signal flow for an example pathway thatconveys traffic that originates in Cleveland (designated Beam 124) anddestined is for Pittsburgh (designated Beam 319) is shown within dashedline 802. Beam Weight Processor 804 will set the coefficients shown inFIG. 5 to the proper values to focus the LHP elements of the phasedarray receive antenna upon the area designated as the Cleveland beam.Terminals, either hubs or subscriber terminals, within the designatedreceive coverage area will broadcast on the designated uplink frequencythrough a left-handed polarized antenna. The received version of thesesignal(s) will be output from the BFN to pathway 1 and will then gothrough the pathway processing as discussed above. The output frompathway 1 will then be input into the transmit beam (feed) formingnetwork. Beam Weight Processor 804 will set the coefficients (as shownin FIG. 6) to the proper values to focus the RHP elements of the phasedarray transmit antenna upon the area designated as the Pittsburgh beam.Terminals, either hubs or subscriber terminals, within the designatedtransmit coverage area will receive on the designated downlink frequencythrough a right-handed polarized antenna.

From the perspective of the satellite, uplink signals are received bythe satellite from transmitting user terminals or from transmittinggateways located in the satellite's receive coverage area. Downlinksignals are transmitted from the satellite to receiving user terminalsor to receiving gateways located in the satellite's transmit coveragearea. From the perspective of the ground equipment (e.g., user terminalsand gateways), the receive coverage area and the transmit coverage areamay be reversed.

FIG. 8B shows a configuration table 810 of the instantaneousconfiguration of the example satellite. Each row corresponds to onepathway. Column 812 includes the number of the pathway, 1 . . . K.Column 816 includes

1. a unique designation of the uplink receive beam, which may be analphanumeric string

2. an alphanumeric ‘arrow’ to designate the direction of signal travel

3. the corresponding downlink transmit beam, which may also be analphanumeric string

In these examples, pathways may cross polarizations, in accordance withtypical industry practice. The convention for the example satellites inthis document is that the first K/2 pathways receive LHP uplink beamsand transmit RHP downlink beams, while the second K/2 pathways receiveRHP uplink beams and transmit LHP downlink beams.

FIG. 8C shows an example timeslot coverage area superimposed on area map820. As discussed previously, pathway 1 has a left-handed polarizeduplink from Cleveland and a right-handed polarized downlink toPittsburgh. The satellite is shown for this pathway, but is omitted forthe other three pathways shown in this figure. For example, pathway 3has a right-handed polarized uplink from Washington, D.C. and aleft-handed polarized downlink to Columbus and is indicated by astraight line on the figure.

At any timeslot in the beam hopping frame, the forward capacity in eachbeam can be calculated by performing a link analysis including thecharacteristics of the ground equipment. By performing a standard linkanalysis, one can calculate the end-to-endcarrier-to-noise-plus-interference ratio, E_(s)/(N_(o)+T_(o)), to aparticular point in the beam. The end-to-end carrier-to-noise ratio,E_(s)/N_(o), typically includes the effects of thermal noise, C/I,intermodulation distortion, and other interference terms on both theuplink and the downlink. From the resulting end-to-endE_(s)/(N_(o)+I_(o)), the modulation and coding may be selected from awaveform library that maximizes the capacity. An example of a waveformlibrary is contained in the DVB-S2 specification, although any suitablewaveform library may be used. The selected waveform (modulation andcoding) results in a spectral efficiency, measured in bps/Hz, to thatspecific point in the beam.

For broadcast data delivery, the spectral efficiency may be computed atthe most disadvantaged point within the beam (e.g., at the worst linkbudget). For multicast data delivery, the spectral efficiency may becomputed at the location of the most disadvantaged user in the multicastgroup. For unicast data delivery, Adaptive Coding and Modulation (ACM)may be employed, where the data delivered to each spot in the beam isindividually encoded to fit the link budget for that particular point inthe beam. This is also the case with the DVB-S2 standard. When ACM isemployed, the average spectral efficiency is relevant. As described inU.S. Patent Application Publication No. 2009-0023384 to Mark J. Miller,filed Jul. 21, 2008, which is incorporated by reference herein in itsentirety, the average spectral efficiency may be generated by computingthe weighted average of the spectral efficiency for every point in thebeam.

The link capacity in a beam may then be calculated as the product of thespectral efficiency (bps/Hz) and the allocated BW in the beam. The totalcapacity during one timeslot in the beam hopping frame is the sum ofcapacities of all the beams that are active during that timeslot. Thetotal capacity is the average of the capacities of the individual beamhopping frames. To maximize total capacity, the beam weights may be setfor all beams and all timeslots to yield the largest antennadirectivity. Beams that are formed in the same timeslot and use the samepolarization and spectrum should be spaced as far apart as possible tomaximize the C/I (and hence minimize the interference into other beams).Under these requirements, it is not uncommon for the spectral efficiencyof each beam to be approximately the same for all beams in alltimeslots. Under this assumption, the system forward capacity can beapproximated in accordance with:

C _(F) =K _(F)·↓_(Hz) ·W  (1)

where η_(Hz) is the spectral efficiency in bps/Hz, K_(F) is the numberof forward beams, and W is the spectrum allocated per beam. Fromequation (1), it can be seen that increasing any of the parametersincreases the capacity.

The maximum number of beam pairs that can be active at one time, K_(F),is essentially determined by the mass and volume budgets of thesatellite. The power limitations on the satellite can also affect thevalue K_(F), but the volume and mass constraints generally are morelimiting.

The satellite architecture disclosed herein is very effective inmaximizing η_(Hz) and W. Due to the small size of the beams, and therelatively small number of beams that can be active at one time (due topayload size, weight, and power limits on K_(F)), all of the allocatedspectrum can be used within each beam with minimal interference betweenbeams. To accomplish this, beams of the same polarization that areactive in the same timeslot should be positioned as far apart aspossible. Alternatively, one could use only a fraction of the spectrumper beam in order to improve the C/I, but due to the beam hopping natureof the present architecture this may result in less capacity. Forexample, suppose each beam used one-half of the available spectrum, orW/2 Hz. Then at any instant in time, there would be half as many beamsthat are co-frequency and present the potential for interference. Theresulting C/I would increase, thus slightly increasing the spectralefficiency, η_(Hz), as C/I is just one of many components in theend-to-end E_(s)/(N_(o)+I_(o)) budget and spectral efficiency generallyvaries as the logarithm of the E_(s)/(N_(o)+I_(o)). But the BW per beamis reduced by a factor of 2, and as expected, the total capacity will bereduced, since the number of beams is limited by the number of signalpathways in the satellite payload.

The spectral efficiency per beam is quite high using the presentarchitecture because active beams can be spaced far apart and thedirectivity of the beams may be large. The former is a result of thelarge coverage areas, the small beam sizes, and the relatively smallnumber of beams that can be active at one time. The latter is a resultof the small beam sizes.

In some embodiments, it may also be desirable to increase the spectralefficiency of a beam by reducing the coverage area of a beam relative toits beam diameter. Typically, the coverage area in spot beam systems mayextend out to the −3 dB contours of a beam or beyond. Some systemsextend the coverage area out to the −6 dB contours. These low contourregions are undesirable for many reasons. First, they may reduce thedownlink E_(s)/N_(o) and reduce the downlink C/I. The reduced C/I is aresult of the reduced signal power (C) and the increased interference(I) as the locations at the edge of a beam are closer to other beams.When computing the weighted average capacity (e.g., for unicast datadelivery) or the edge of beam capacity (e.g., for broadcast datadelivery), this large antenna roll off at the edge of the beam mayreduce capacity. In accordance with the present architecture, however,the beam coverage area may be constrained to regions within the beamwhere the antenna roll-off is much less, such as approximately −1.5 dB.This may increase the spectral efficiency since there are no locationsin the beam at the −3 to −6 dB levels relative to beam center. The beamcoverage area may be smaller, however, but this is compensated for byhopping to more areas within the beam hopping frame (e.g., increasingthe number of timeslots per frame).

The link capacity may be enhanced by:

-   -   Use of the full allocated spectrum per beam.    -   Use of small beams resulting in high beam directivity and large        uplink E_(s)/N_(o) and ultimately better return link spectral        efficiency.    -   Large service areas realized by hopping small beams around in a        beam hopping frame with many slots per frame resulting in a        relatively small number of beams active at one time and spread        over a large service area. Thus, beams can be spaced far apart        resulting in high C/I values leading to higher spectral        efficiency.    -   Defining smaller beam coverage areas such that the edge of beam        roll off is relatively small, such as approximately −1.5 dB.        This increases the average spectral efficiency, and the capacity        per beam, as the relatively high roll-off beam locations that        degrade both uplink C/I and E_(s)/N_(o) have been eliminated.

FIG. 9 shows illustrative process 900 for supporting satellitecommunication in accordance with the present invention. Illustrativeprocess 900 corresponds to one pathway (such as the pathway shown withindashed line 802 of FIG. 8A), which can service a forward and/or returnlink of a hub-spoke satellite communication system, such as satellitecommunications system 100 (FIG. 1). It should be understood that inpractical applications, a large number of these pathways will be activeduring a single timeslot dwell time, and thus a corresponding largenumber of these processes will be operating in parallel.

At step 902 of FIG. 9, a current frame is selected. For example, beamweight processor 414 (FIG. 4) may receive one or more pre-computedweight sets via data link 416 (FIG. 4). The frame selected at step 902will include one or more timeslot definitions and one or more weightmatrices. For example, beam weight processor 414 (FIG. 4) or affiliatedhardware may provide the bulk storage for a plurality of beam hoptimeslot definitions and a plurality of weight matrices. A weight matrixmay include the set of all complex weight vectors used for transmissionand reception of all beams in one timeslot. A weight vector may includethe group of L_(tx) or L_(rx) individual complex weights used by aphased array to create one beam during one timeslot. A beam hop timeslotdefinition may include the set of all pathway gains of all beams in onetimeslot and may specify all dwell times associated with the timeslot.

At step 904, a first timeslot definition and a first weight matrix areselected for the current frame. For example, sequential logic 706 (FIG.7) of beam weight processor 700 (FIG. 7) may include a counter forselecting a timeslot. Timeslot definitions and/or weight matrices mayalso include location data used to create one or more receive beams, oneor more transmit beams, or both. For example, the location data mayinclude the set of all complex weight vectors used to generate theactive beams for the timeslot.

At step 906, a determination is made whether the communication is partof a forward link or a return link. As explained above, in a hub-spokesystem, a gateway (e.g., gateway 115 of FIG. 1) may communicate withuser terminals (e.g., user terminals 130 of FIG. 1) using downstream(e.g., forward) links, while user terminals (e.g., user terminals 130 ofFIG. 1) may communication with a gateway (e.g., gateway 115 of FIG. 1)using upstream (e.g., return) links. The gateway may service its ownuplinks and downlinks to and from a satellite (e.g., satellite 105 ofFIG. 1). The gateway may also schedule traffic to and from the userterminals. Alternatively, the scheduling may be performed in other partsof the satellite communications system (e.g., at one or more networkoperations centers (NOC) and/or gateway command centers). For example,in some embodiments, the gain settings included in the frame definition(e.g., as part of each timeslot definition) may be used to determinewhether a communication is a forward link or a return link.

If, at step 906, a forward link is being processed, then at step 908 thegain for the pathway may be adjusted, if necessary, to support a forwardlink. For example, a selectable gain channel amplifier may provide thegain setting for the pathway in use, as shown in FIG. 4. The gainsetting can be determined from the first timeslot definition. At step910, a receive beam signal is created for the duration of the timeslotdwell time. For example, a satellite-based receive phased arrayincluding a receive beam forming network (e.g., BFN 410 of FIG. 4) maybe configured to create one or more receive beams on the satellite forthe duration of the timeslot dwell time. The receive beams may be usedto receive one or more multiplexed signals (e.g., a multiplexed signalfrom a gateway, such as gateway 115 (FIG. 1)) destined for a pluralityof terminals. For example, the multiplexed signal may be destined foruser terminals 130 (FIG. 1). At least some of the individual componentsignals of the multiplexed signal can differ in content, for example, ifdestined for different user terminals. The multiplexed signal may bemultiplexed using any suitable multiplexing scheme, including, forexample, MF-TDM, TDM, FDM, OFDM, and CDM. In general, TDM is used forsimplicity.

If, at step 906, a return link is being processed, then at step 912 thegain may be adjusted, if necessary, to support a return link. Forexample, a selectable gain channel amplifier may provide independentgain settings for the pathways in use, as shown in FIG. 4. The gainsetting can be determined from the first timeslot definition. At step914, a receive beam signal is created for the duration of the timeslotdwell time. For example, a satellite-based receive phased arrayincluding a receive beam forming network (e.g., BFN 410 of FIG. 4) maybe configured to create one or more receive beams on the satellite forthe duration of the timeslot dwell time. The receive beam is used toreceive one or more multiple access composite signals (e.g., a compositesignal derived from a plurality of terminals, such as user terminals 130(FIG. 1)) destined for a gateway (e.g., gateway 115 (FIG. 1)). Themultiple access composite signal may be formed using any suitablemultiple access scheme, including, for example, MF-TDMA, TDMA, FDMA,OFDMA, and CDMA. The multiple accesses during the slot period may be allrandom access, all scheduled transmissions, or a mixture of randomaccess and scheduled transmissions.

At step 916, a satellite-based transmit phased array including atransmit beam forming network (e.g., BFN 412 of FIG. 4) is configured togenerate one transmit beam signal for the duration of the timeslot dwelltime. The transmit beam signal is derived from the received multiplexedor multiple access composite signal using a bent-pipe pathway on thesatellite. For example, one or more of frequency conversion, filtering,and selectable gain amplification may be performed on the receivedsignal to create the transmit signal.

At step 918, the timeslot dwell period has passed and a determination ismade whether there exist additional timeslots in the frame definition toprocess. For example, sequential logic 706 (FIG. 7) may be instructed toautomatically loop timeslots included in a frame definition at theconclusion of each frame. As described above, frame definitions andweight sets may be time-varying and dynamically adjusted locally at thesatellite (e.g., by sequential logic 706 (FIG. 7) or computer 702 (FIG.7), or remotely at a ground facility using data link 416 (FIG. 4)). If,at step 918, there are more timeslots to process, then at step 920 thenext timeslot may be selected for processing. For example, a newtimeslot may be selected immediately after the timeslot dwell time ofthe timeslot selected in step 904 has elapsed. In practice, multipletimeslot definitions and multiple weight sets may be loaded into memory704 (FIG. 7) of BWP 700 (FIG. 7) and timeslot definitions and weightmatrices may be accessed by following a pointer, for example, of alinked list or other data structure. Illustrative process 900 may thenreturn to step 906 to create new receive beam signals and generate newtransmit beam signals for the new timeslot dwell time. If, at step 918,a determination is made that there are no more timeslots to process inthe frame, then at step 919 a determination is made whether or not a newframe definition or a new weight set has been received. For example, acommand to change frame definitions and/or weight sets may have beenreceived (e.g., from computer 702 (FIG. 7) or from a remote scheduler)or a new frame definition and/or a new weight set may have been uploadedto the satellite. If, at step 919, neither a new frame definition or anew weight set has been received, then the current frame may beprocessed again (e.g., automatically repeated). If a new framedefinition or a new weight set has been received, this new framedefinition or this new weight set may be selected for processing.

As an example of the high capacity offered, consider a system with thefollowing parameters:

-   -   A 5.2 m reflector on satellite with a 15 kW power available for        use by the payload.    -   Ka band operation with an allocated spectrum of 1.5 GHz on each        of 2 polarizations.    -   Payload volume and mass constraints support up to 100 pathways,        each 1.5 GHz wide (using all spectrum on one polarization)        active at one time. Assume 50 pathways are used for forward        traffic and 50 pathways for return traffic, yielding a total of        50*1.5 GHz=75 GHz of spectrum in each direction.    -   A 75 cm user terminal. For large beam spacing (large coverage        area), the resulting forward link budget supports a spectral        efficiency of about 3 bps/Hz resulting in about 225 Gbps of        forward capacity    -   The return link budget supports 1.8 bps/Hz resulting in 135 Gbps        of return link capacity. The total capacity is about 360 Gbps.

Flexible Allocation Between Forward and Return Capacity

As shown in FIG. 4, the satellite contains K generic sets of pathways.Each pathway consists of a formed receive beam and a formed transmitbeam which are interconnected by path electronics nominally consistingof filters, a downconverter, and amplifiers. In accordance with oneembodiment of the subject invention employing a hub spoke systemarchitecture, these K pathways can be used to flexibly and programmablyallocate capacity between the forward direction (GW to user terminals)and the return direction (user terminals to GW). The allocation isflexible in that that the total resources can be split amongst forwardand return in any proportion desired resulting in any desired ratiobetween forward and return channel capacity. The allocations areprogrammable in that the splitting of the resources can be altered atevery frame, thus rapidly changing the ratio between forward and returncapacity. This is particularly useful for changing the forward/returncapacity allocation to accommodate new and evolving applications usingdata/information transfer over a satellite system.

The flexible capacity allocation is accomplished by a flexibleallocation of resources in the satellite architecture. The resources ofinterest here are the number of physical pathways on the satellite andthe time fractions in each beam hopping frame. Two approaches arepresented for flexible capacity allocation. Approach 1 flexiblyallocates time resources, where approach 2 flexibly allocates HWresources.

Approach 1: Flexible Allocation of Time Resources

In this approach, one or more pathways are allocated for use in theforward direction a fraction of the time, α_(F). The remainder of thetime (1−α_(F)) it is used for return traffic. Suppose there are Q fixedlength time slots in the beam hopping frame. Then for Q_(F)≈α_(F) Q outof the Q time slots the pathway will be configured for forward traffic.Alternatively, the forward time slots and return time slots could varyin length by the same ratio, although the examples that follow will belimited to the case of fixed length time slots.

Configured for forward traffic means that the Rx beam uses a weightvector that has the beam pointed to a GW site, the transmit beam uses aweight vector that has the beam pointed at a user service area, and thechannel amplifier associated with the pathway is set to yield thesatellite net gain that is consistent with a forward channel. Configuredfor return traffic means that the Rx beam uses a weight vector that hasthe beam pointed to a user service area, the transmit beam uses a weightvector that has the beam pointed at GW site, and the channel amplifierassociated with the pathway is set to yield the satellite net gain thatis consistent with a return channel.

In many, if not most, hub spoke applications the user terminal and GWterminal sizes are quite different. For example, the GW terminal mightbe 7 m in diameter with 100's of Watts of output power capability in theHPA behind it and the user terminal may be less than 1 m in diameterwith only several Watts of output power capability in the HPA behind it.In such scenarios, it is common for the desired net electronic gain ofthe satellite to be different in the forward direction from the returndirection. Thus, in general, the channel amplifier in a pathway needs tobe configured for different gains in the forward and return directions.

In an extreme example, let Q_(F)=Q for all pathways. The result is aForward Link Only (FLO) system in which all capacity is allocated to theforward link and no capacity is allocated to the return link. This isuseful for a media broadcast system. However, the same satellite can beconfigured (via uploading a different beam weight set and channelamplifier gain set) to allocate 75% (for example) of the time slots forforward transmission and 25% for return transmission. This would resultin a forward direction capacity of 75% of the FLO example and a returncapacity of 25% of the maximum of what could be achieved. In general,let C_(F) _(_) _(max) be the forward channel capacity with all timeslots allocated to the forward direction and let C_(R) _(_) _(max) bethe return channel capacity with all time slots allocated to the returndirection. Then for Q_(F) forward time slot allocations andQ_(R)=Q−Q_(F) return channel time slot allocations, the forward andreturn capacity is

$\begin{matrix}{{C_{F} = {{\frac{Q_{F}}{Q} \cdot C_{F\_ max}}\mspace{14mu} {and}}}{C_{R} = {\left( {1 - \frac{Q_{F}}{Q}} \right) \cdot C_{R\_ max}}}} & (2)\end{matrix}$

where QF can assume any value from 0 (all return traffic) to Q (allforward traffic). It is clear from (2) that the allocation of capacitybetween forward and return can take on any arbitrary proportion limitedonly by the value of Q, the number of time slots per beam hopping frame.For reasonable sizes of Q, such as Q=64, this limitation is not verylimiting as it allows allocation of capacity in increments of 1/64 ofthe maximum value.

In this approach, all K pathways are used exclusively for forwardtraffic or exclusively for return traffic at any instant of time. Therequirements for the total number of GW locations can be determined asfollow. Let there be K pathways each using W Hz of spectrum on a singlepolarization. Furthermore, let there be N_(GW) gateway sites, eachcapable of using W Hz of spectrum on each of two polarizations. At anyinstant of time, the total user link spectrum is KW Hz, which is beingused for either forward link or return link transmissions (but neverboth). The total feeder link spectrum utilized at any given instant is2N_(GW)W, which is also used for either forward link transmission orreturn link transmission, but never both. Equating the two spectrumquantities results in the required number of GWs, N_(GW)=K/2.

This approach is inefficient since a GW is not both transmitting andreceiving 100% of the time. The fraction of time a GW spendstransmitting added to the fraction of time that the GW spends receivingis equal to 1. However, a GW could both transmit and receive 100% of thetime and is thus being inefficient and underutilized.

Such an approach is said to be synchronized, as illustrated in FIG. 12Awhich shows a 50%-50% time resource allocation between the forward andreturn link for each pathway.

The pathways are synchronized in that they all service the forward linkat some times and all service the return link at other times. As can beseen in the figure, the total feeder link spectrum used is always KW Hz,and it is always either all forward link spectrum or all return linkspectrum. As discussed above, this synchronized system requires K/2GW's.

FIG. 12B shows an example synchronized time allocation system on ademonstration 8 pathway satellite with 8 user beams and 4 GW's. In Slot1, FIG. 12B, all four gateways GW1, GW2, GW3 and GW4 are transmitting tobeams B1-B8 as shown in the slot configuration table. Below the slots,the pathway (PW) usage of the slot is detailed. In Slot 1, all 8pathways are used for forward links, thus the entry 8F. In Slot 2,terminals in all the beams are transmitting to their respectivegateways, so the pathways usage is denoted 8R. To the right of thetable, the slot usage is listed for each pathway. For all pathways, thefirst slot is forward and the second slot is return, so each slot usageentry is FR.

In this example, the gateways may be autonomous from each other,although equivalently the transmit gateway to a user beam could bedifferent than the receive gateway for that user beam. In that case, thegateways would need to cooperate in order to provide coherent two-waycommunication to and from user terminals. Note that in all suchsynchronized cases, half-duplex (transmit and receive at differenttimes) user terminals could be deployed, as all the user beams can bescheduled such that the user terminal transmit slots do not overlap withcorresponding receive slots.

The approach can be improved by interleaving the forward and return timeallocations as shown in FIG. 13A. The forward and return timeallocations for each pathway are structured such that at any instant oftime, half of the pathways are used for forward traffic and half areused for return traffic. This results in the total feeder link spectrumrequirement at any instant of time being the same (KW Hz), but it isevenly split between the forward link and the return link. Since a GWhas 2 W Hz of spectrum to use in forward direction and 2 W Hz to use inthe return direction, the total number of GW's required is K/4. This ishalf the number of GW's as required when synchronizing the forward andreturn time allocations, and hence the preferred way to operate.

FIG. 13B shows a 50%-50% time allocation example with a similar 8-pathsatellite and 8 user beams as in FIG. 12B. Now, however, only two GW'sare required, GW1 and GW2. In FIG. 13B, GW1 is transmitting LHP to B1(which receives RHP) and transmitting RHP to B2 (which receives LHP).Due to the separate polarization, there is no signal interferencebetween beams, even though they are physically adjacent and could evenoverlap partially or totally. At the exact same time (during that firsttime slot), the terminals in B7 and B8 are transmitting to GW1. Alsoduring this first time slot of FIG. 13B, GW2 is transmitting to B3 andB4, while B5 and B6 are transmitting to GW2. In the second slot, as inFIG. 12B, the transmission directions are reversed from those of slot 1.Comparing FIG. 13B to FIG. 12B, it can be seen that each user beam hasexactly the same number of transmission and reception opportunities.Note that in this specific case, half-duplex user terminals could bedeployed, as the user beams are scheduled such that the user terminaltransmit slots do not overlap with corresponding receive slots. Adifferent schedule could be used that would also achieve the 50%-50%time allocation, but with user beam transmit and receive slot overlap,possibly requiring that user terminals operate full-duplex, where theycould transmit and receive at the same time.

In this example, again the gateways may be autonomous from each other,since each user beam has a single gateway for both its forward (to theuser beam) and return (to the gateway) transmissions. Also equivalentlyto the scenario of FIG. 12B, the transmit gateway to a user beam couldbe different than the receive gateway for that beam. In that case, thegateways would need to cooperate in order to provide coherent two-waycommunication to and from user terminals.

The example shown in FIGS. 13A-B employed 50%-50% time resourceallocation. The example in FIG. 14A shows an interleaved time allocationapproach for a 75%-25% time allocation between the forward and returntraffic. In this example, 75% of the pathways are used for forwardtraffic at each instant of time. The remaining 25% are used for returntraffic. Each individual pathway is also used for forward traffic during75% of the beam hopping frame and return traffic during 25% of the beamhopping fame. The result is that at any and every instant of time, theBW used for forward traffic is 3 KW/4 and the BW used for return trafficis KW/4. Since each GW can use 2 W Hz of bandwidth for forward trafficand 2 W Hz of bandwidth for return traffic, the total number of GW'srequired is 3K/8 and is limited by the forward link BW utilization. Thisnumber is still smaller than the K/2 value required for the synchronizedapproach for a 50%-50% time resource allocation, as shown in FIGS.12A-B.

FIG. 14B shows the 4 time slots of an example system including the eightuser beams and four gateways of FIG. 12B. As in that example, gatewayseither transmit or receive during each slot, but never both transmit andreceive in the same slot. The usage summary at the bottom of theconfiguration table shows that each slot has 6 forward (GW-user)pathways and 2 return (user-GW) pathways.

In the first slot, user terminals in B1 and B2 transmit to GW1, whileall other user terminals receive. In the second slot, the user terminalsin B7 and B8 transmit, while the others receive. In the third slot, theuser terminals in B3 and B4 are the only ones to transmit, while in thefourth slot, the user terminals in B5 and B6 are the only transmitters.Tabulation of the slots will confirm that each user beam has 3 forwardpathways from a single gateway to the beam, and one return pathway fromthe user beam to that same gateway. In this case, K/2=4 gateways areused, although the minimum number of gateways is 3K/8=3 gateways.

If 100% of the traffic were allocated to the forward link, all pathwayswould be used for forward traffic 100% of the time. This would result inthe total forward spectrum of KW Hz and the required number of GW'swould be K/2, the same number as in the synchronized approach.

In the general case, each pathway is allocated to be a forward pathwayfor a fraction α_(F) of the time in the beam hopping frame. Theallocations are interleaved with the objective of having a fractionα_(F) of the K total pathways operating as forward pathways at eachinstant of time. The remainder, K(1−α_(F)), would be operating as returnlink pathways. At each instant of time, the required forward linkspectrum is KW α_(F) and the required return link spectrum isKW(1−α_(F)). Hence the total number of required GW's isN_(GW)=Max(α_(F), 1−α_(F))K/2. Note this may require coordination amongthe GW's.

Approach 2: Flexible Allocation of Hardware Resources

In this approach, any single pathway is either dedicated entirely (alltimes slots in the beam hopping frame) to forward link transmissions ordedicated entirely to return link transmissions. What is flexible is thenumber of pathways that are dedicated to forward pathways and the numberof pathways that are dedicated to return pathways. This is illustratedin FIG. 15A for an example allocation of 75% of the pathways to forwardlinks and 25% to return links.

FIG. 15B shows the timeslots for a 75%-25% pathway allocation 4 slotframe for the example 8 pathway satellite communication system asdiscussed previously. Here, the pathways are identified by number in themap view. Pathway 1 (LHP→RHP) and Pathway 5 (RHP→LHP) are dedicated toreturn traffic, while the remaining pathways are dedicated to forwardtraffic.

In slot 1, GW1 receives data from user beams B1 and B2, while all threegateways transmit to the remaining user beams. In slot 2, B3 and B4transmit to GW1, while all three gateways transmit to the remaining userbeams. In slot 3, B5 and B6 transmit to GW1, while all three gatewaystransmit to the remaining user beams. In slot 4, B7 and B8 transmit toGW1, while all three gateways transmit to the remaining user beams.

Consider one polarization of this example two-pole system. We still havethe three gateways, GW1-GW3 (each operating in one of the two availablepolarities), but now only consider user beams B1-B4 and pathways 1-4.There are still 4 slots per frame and thus 4 pathways×4 slots=16 totalslots available. We have allocated 75% (12) of these slots to forwardtraffic and 25% (4) of these slots to return traffic. The 4 return slotsfill the entire frame exactly. The 12 forward slots need to bedistributed across the 4 user beams, so each user beam gets 3 slots.These same 12 forward slots, however, need to be distributed across 3gateways, so each gateway must fill 4 forward slots. Thus, there cannotbe a one-to-one mapping between gateways and user beams such that allthe traffic for any user beam passes through the same gateway.

Careful attention to the number beams, slots, gateways and pathways canprovide flexibility in the mapping of gateways to user beams. FIGS.15C-E show two more example embodiments of flexible allocation ofhardware resources. Here, there are 6 user beams that require a 75%-25%pathway allocation in the example 8 pathway satellite, 3 gatewaycommunication system as discussed previously. Since there are only 6user beams B1-B6, only 3 time slots are required. The user terminalswill generally operate in full-duplex (simultaneous receive andtransmit) mode during their active beam hopping time slots. Now thereare 4 pathways×3 slots=12 slots to be allocated per polarity. 75% of 12(9) slots are used for forward traffic, while 25% of 12 (3) slots areused for return traffic. The 3 return slots again fill one frame,corresponding to the one pathway allocated for return traffic perpolarity. Now, however, the 9 forward slots (3 per pathway) per polaritycan be divided such that there are exactly 3 slots per gateway and 3slots per user beam, thus allowing a one-to-one mapping between userbeams and gateways.

In FIGS. 15C and 15D, both polarities are depicted. Forward pathways 2-4and 6-8 are each dedicated to a single gateway: pathways 2 and 6 (forthe two polarities) of Gateway 2, pathways 3 and 7 for Gateway 3 andpathways 4 and 8 for Gateway 1. In FIG. 15C, the return pathways areshared among the three gateways such that each gateway receives from thesame beams to which it transmits, thus implementing a one-to-one mappingbetween user beams and the gateways that service them. Alternatively, inFIG. 15D, the return pathways are all directed to Gateway 1. In thiscase, Gateway 1 is considered a shared receive gateway and gateways 2and 3 can operate half-duplex as transmit only. In this shared receivegateway embodiment, a number of gateways transmit to a number of userterminals, while those user terminals only transmit (if they transmit atall) to a single gateway, typically one of the transmit gateways. FIG.15E shows the first time slot of the system of either 15C or 15D, as itis the same in both cases.

The shared receive gateway can have utility, for example, if there areuser terminals that transmit requests for information that is located atone gateway, or if one gateway is the interface between the groundnetwork of gateways and an external network. In this case, having alluser terminals request the information directly from that gateway willavoid the problem of having the other gateways forward requests to thatinterface gateway.

The reverse is also possible: a shared transmit gateway system whereuser terminals, perhaps sensor terminals, transmit a large amount ofinformation, but only need to receive a small amount. For example, a25%-75% time allocation could be implemented by switching the directionof the beams in FIG. 15B. Thus, GW1 would be the common transmitter forall the service (user) beams. In these shared gateway embodiments,half-duplex gateways can be deployed if the system operator has abackbone network that connects the gateways such that traffic can bedirected and scheduled properly.

Let K_(F) be the number of forward pathways and K_(R) be the number ofreturn pathways where K_(F)+K_(R)=K is the total number of pathways.Since each pathway is always used entirely in the forward or returndirection, there is no need to dynamically change the net electronicgain through the pathway on a time slot by time slot basis. Hence,dynamic adjustment of the channel amplifier gain on a slot-by-slot basismay not be required.

By setting K_(F)=K and K_(R)=0, we have all forward traffic, (FLO). Bysetting K_(R)=K and K_(F)=0, we have all return traffic, (Return LinkOnly or RLO). In general, the capacity allocation is each direction is,

$\begin{matrix}{{C_{F} = {{\frac{K_{F}}{K} \cdot C_{F\_ max}}\mspace{14mu} {and}}}{C_{R} = {{\frac{K_{R}}{K} \cdot C_{R\_ max}} = {\left( {1 - \frac{K_{F}}{K}} \right) \cdot C_{R\_ max}}}}} & (3)\end{matrix}$

where K_(F) can assume any value from 0 (all return traffic) to K (allforward traffic). It is clear from (3) that the allocation of capacitybetween forward and return can be take on any arbitrary proportionlimited only by the value of K, the number of pathways on the satellite.For reasonable sizes of K, such as K=100, this limitation is not verylimiting as it allows allocation of capacity in increments of 1/100 ofthe maximum value.

In this approach, at any instant of time the total user link spectrumused in the forward direction is K_(F)W. In the return direction, thetotal spectrum used is K_(R)W. Again, it is assumed that each GW has WHz available for use on each of two polarizations. The total feeder linkspectrum available for use is 2N_(GW)W in each direction (forward andreturn). Therefore the number of cooperating (not autonomous) GW'srequired is, N_(GW)=Max(K_(F),K_(R))/2, which is the same as approachone when careful assignment of the Transmit and Receive slots was chosento minimize the GW count. However, approach 2 has the advantage of notneeding to dynamically change the net gain of the pathway during thebeam hopping frame to accommodate dynamic changing between forward andreturn configurations. FIG. 17 shows an illustrative chart 1700 of thenumber of cooperating gateways required versus the number of forwardpathways allocated when K=100. As shown in FIG. 17, the number ofcooperating gateways required is minimum when K_(F)=K_(R), while thenumber of cooperating gateways required is maximum for RLO (i.e.,K_(F)=0) and FLO (i.e., K_(R)=0).

In all of the discussed approaches, it should be clear that the forwardlink and return link can be operated as two independent transmissionsystems. The allocation of capacity between the two transmission systemscan be divided up in just about any proportion desired, as possiblylimited by K or Q. Then each transmission system can independentlyspread its capacity around the coverage area in any way desired byappropriate setting of the weight vectors that create the user beams ineach time slot. Generally, one would set the coverage area for theforward link and return links to be the same physical area. Thisprovides every point in the coverage area with opportunities forreception of forward link data and transmission of return link data. Ingeneral, these opportunities will not always occur in the same timeslots. It can also be seen that the ratio of forward to return trafficneed not be the same at every point in the coverage area. This allowsthe ratio of forward to return traffic to be customized in each beamcoverage area. The mechanism for customizing this ratio is theadjustment of the number (and/or size) of forward and receive time slotsallocated to each physical beam location.

It is also possible to have non-congruent coverage areas for forward andreturn link service. This is depicted in FIG. 16A. The forward linkcoverage area is the union of the coverage area of the individualforward link user beam formed during a beam hopping time frame.Likewise, the return link coverage area is the union of the coveragearea of the individual return link user beam formed during a beamhopping time frame. The union of the forward and return coverage areascan be broken into 3 regions. Region 1 is the area where the beam weightset provides forward link beams but no return link beams. This regioncould support forward link traffic only. Region 2 is the area where thebeam weight set provides return link beams but not forward link beams.This region could support return link traffic but not forward linktraffic. Region 3 is the region where the beam weights provide bothforward and return beams, although not necessarily in the same timeslot. Both forward and return link traffic can be supported.Furthermore, the ratio of forward to return capacity can be customizedin each physical beam location within region 3.

A simple single gateway, 4 pathway system is illustrated in FIG. 16B.Here, forward link Region 1 contains Beams 1 and 2, return link Region 2contains Beams 5 and 6, while bi-directional Region 3 contains Beams 3,4, 7 and 8. This illustrates that while Region 3 was shown in FIG. 16Aas a single logical zone, there is no requirement that the beamscomprising Region 3 be contiguous. In fact, Regions 1 and 2, shown inthis example as contiguous, could also have been comprised of a numberof distinct areas.

In Slot 1, the gateway transmits to the terminals in Region 1, B1 andB2, and receives from the terminals in Region 2, B5 and B6. Theterminals in Region 3 are inactive during this slot, while the terminalsin Regions 1 and 2 are inactive during the remaining slots. In Slot 2,the gateway transmits to terminals in B3 and B4 and receives fromterminals in B7 and B8. In Slot 3, the gateway receives from terminalsin B3 and B4 and transmits to terminals in B7 and B8.

The present invention provides a flexible high-capacity satellitecommunications architecture. Characteristics of this architecture mayinclude one or more of the following:

1. high capacity;

2. flexible allocation between forward and return capacity;

3. flexible capacity distribution and coverage areas;

4. re-configurable coverage areas and capacity allocation;

5. flexible GW locations, for example, using beam hopping to enable GW'sto occupy the same spectrum and the same location as user beams; and theability to move GW locations over the lifetime of the satellite;

6. incremental GW rollout;

7. orbit slot independence;

8. dynamic equivalent isotropically radiated power (EIRP) allocationacross GW's to mitigate rain fade, for example, where marginrequirements are based on a sum of rain fade on all diverse paths ratherthan on statistics of an individual path;

9. operation with half-duplex terminals; and

10. operation with reduced redundancy payload hardware.

Characteristics (1) and (2) have been described. Further details ofcharacteristics (3) through (10) are provided below.

Flexible Capacity Distribution and Coverage Areas

A small number of cells can be active at any instant of time. In oneexample, K_(F)=40 to 60 transmit user beams (user terminal downlink).Beam weight vectors can be dynamically changed per an uploaded schedule.Take an example where the total number of user cells equals K_(F)×Q,where Q=number of timeslots and 1≦Q≦64. Here, the coverage area isincreased by a factor of Q. The average duty cycle of a beam=1/Q. Theforward link speed to a beam is reduced by a factor of Q. It ispreferable for the user terminal to be able to demodulate all carriersin the W Hz bandwidth. For W=1500 MHz, η_(Hz)=3 bps/Hz, and Q=16, theaverage downlink speed to a user terminal is about 281 Mbps.

Turning to the return link, in one example, K_(R)=40 to 60 receive userbeams (user terminal uplink). Beam weight vectors can be dynamicallychanged per an uploaded schedule. Take an example where the total numberof user cells equals K_(R)×Q, where Q=number of timeslots and 1≦Q≦64.Here, the coverage area is increased by a factor of Q. The average dutycycle of a beam=1/Q. The return link speed to a beam is reduced by afactor of Q. It is preferable for the user terminal to use a burst HPAcapable of high peak power but lower average power. For 12 W peak HPAwith 3 W average power limit, 40 Msps uplink, 2.25 bits/sym, and Q =16,the average uplink speed from a user terminal is 5.625 Mbps.

The flexible high-capacity satellite communications architecturedescribed herein may also provide non-uniform distribution of capacity.Capacity can be allocated to different cells in near arbitraryproportions by assigned differing numbers of slots per cell. Again,there are Q timeslots in a beam hopping frame. Each cell uses q_(j)timeslots, such that

$\begin{matrix}{{\sum\limits_{j = 1}^{J}q_{j}} = Q} & (4)\end{matrix}$

where J is the number of locations that a beam hops to in the beamhopping frame. Capacity in each cell is:

$\begin{matrix}{C_{j} = {C_{b}\frac{q_{j}}{Q}}} & (5)\end{matrix}$

where the instantaneous capacity per beam=C_(b).

An example of beam hopping with non-uniform distribution of capacity isshown in FIGS. 18A-C. FIG. 18A shows an illustrative beam hop pattern1800 of a single beam for 8 non-uniform timeslot dwell times of a beamhopping frame. In the example, Q=32 and C_(b)=4.5 Gbps. The celllocations in the beam hop pattern 1800 are shown as contiguous for easeof illustration. FIG. 18B shows an illustrative timeslot dwell timetable 1810 for the beam hop pattern 1800. For each of the 8 timeslotdwell times of the timeslot dwell time table 1810, the number oftimeslots q_(j) assigned to the corresponding cell location and the areacapacity C_(j) in Mbps is shown. FIG. 18C shows an illustrative beamhopping frame 1820 for the timeslot dwell time table 1810. The beamhopping frame 1820 includes K beams. The non-uniform timeslot dwelltimes for beam #1 of the beam hopping frame 1820 match the dwell timesillustrated in the timeslot dwell time table 1810. It is preferable tohave all the beams change locations at the same time. This minimizes thebeam-beam interference as each beam only overlaps in time with K−1 otherbeams. However, the system can operate without this constraint. Morebeams can then interfere with each other, and the beam locations shouldbe chosen with this in mind.

Re-configurable Coverage Areas and Capacity Allocation

Beam locations are defined by the weight vectors used in the beamforming networks. Capacity per cell is set by the duration of the beamhopping frame the beam stays pointed at a cell (dwell time). Both beamweight vectors and dwell times (e.g., as beam hop frame definitions) canbe stored in the beam weight processor (BWP). These values can beuploaded to the BWP by a data link from the ground. Both the beamlocations (coverage area) and dwell time (capacity allocation) can bechanged. For example, the beam locations and/or the dwell times can bechanged occasionally by uploading new weight sets and new beam hop framedefinitions, or frequently in response to daily variations (e.g.,capacity shifting to match the busy hour) by commanding the BWP to useone of several pre-stored weight sets and beam hop frame definitions.One weight set contains beam weights and one beam hop frame definitioncontains dwell times for all the beams in all time slots in a beamhopping frame.

Flexible Gateway Locations

Gateways can be placed outside of a service area or in a service area atthe cost of a small increase in the number of GW's. To facilitatemapping gateway locations, one can use the number of colors availablefrom the GW's. The total number of colors=time colors×polarizationcolors×frequency colors. Take an example with Q=4, W=1500 MHz (fullband), and dual polarization. The total number of colors=4 times×2poles×1 frequency=8. The number of GW's, N_(GW), is determined by

$\begin{matrix}{{{\sum\limits_{i = 1}^{N_{GW}}C_{i}} \geq {K \cdot Q}} = {M = {\# \mspace{14mu} {of}\mspace{14mu} {user}\mspace{14mu} {beams}}}} & (6)\end{matrix}$

where C_(i)=the number of colors serviceable by GW #i.

FIG. 19A shows illustrative gateway locations and user beam locationsfor an example with 23 GW's (22 operation+1 utility GW). The user beamlocations are shown as cells and the gateway locations are shown asdashed circles in the map 1900 of FIG. 19A. FIG. 19B shows anillustrative gateway table 1910 for the map 1900. The gateway table 1910shows, for each gateway, the gateway location, the number of beam issues(i.e., the number of colors unusable), and the number of colorsserviceable by the gateway, C₁. For K=40, Q=4, M =160 beams, and the C,illustrated in the gateway table 1910, ΣC_(i)=168 >160. Thus, for thisexample, the system can operate with any 22 out of the 23 gateways.Placing all the gateways with no beam infringements would require K/2=20gateways. In this example, only 2 additional gateways are required toallow some spatial overlay between GW's and user beams.

In an extreme example, all the gateways are located in the service area.Here, K=40, Q=24, and M=960 beams for full CONUS coverage and a hopdwell= 1/24th of the beam hopping frame for all beams. The total numberof colors is 48=24 times×2 poles. If the GW's were located away from theservice area, the minimum number of GW's would be 20. However, for thisextreme example with all gateways located in the service area, themaximum number of colors unusable is assumed to be 7. Thus,C_(i)≧41=48−7 for all GW's. It is further assumed that 6 GW's arelocated where the number of unusable colors is ≦4 (e.g., coverageboundaries such as coastal regions). For these 6 GW's, C_(i)=48−4=44.The number of GW's required is equal to 23, whereΣC_(i)=(6×44)+(17×41)=961≧960. This results in a 15% increase (i.e.,from 20 to 23) in gateways required, but with complete flexibility inthe location of 17 out of 23 GW's, all of which are within the servicearea.

Flexibility in gateway locations can also be achieved with non-uniformhop dwell times. The number of GW's required is defined by a similarequation

$\begin{matrix}{{\sum\limits_{j = 1}^{N_{GW}}C_{j}} \geq {K \cdot Q}} & (7)\end{matrix}$

where C_(j)=total number of useable hop dwell periods by GW j. Themaximum possible value of C_(j) is 2Q (i.e., 2 polarization colors, 1frequency color). The optimum placement of GW's is, first, in regions ofno service (i.e., C_(j)=maximum value), and second, in cells of low hopdwell time and next to cells of low hop dwell time. Placing GW'saccordingly will generally result in even fewer additional GW's,compared to the examples above where the hop dwell times are uniform.

FIG. 19C shows illustrative placements 1920 of gateway locations. Inthis example, Q=32 hop dwells per beam hopping frame, there are 2polarization colors, and 1 frequency color. The first placement, whereC_(j)=64=maximum value, places the GW in a region of no service. Theother three placements, where C_(j)<64, place the GW's in cells of lowhop dwell time and next to cells of low hop dwell time.

Incremental GW Rollout

Incremental GW rollout is described for an example system with K=40,Q=4, and N_(GW)=20. The number of beams M=160, and the average dutycycle=1/Q=25%. In a first example, if service is started with 1 GW (K=2pathways), 1 GW services 2 beams at a time. Setting the number of timeslots Q=80 provides all 160 beams. However, the resulting dutycycle=1/80. Thus, in this first example, there is a reduction in speedand capacity. The duty cycle can be increased as the number of GW'sincrease.

In a second example, if service is started with 4 GW's and only 40beams, the resulting coverage area is 25% of the initial coverage area.Note that it can be any 25%. With K=8 pathways, setting Q=5 provides 40beams, with a duty cycle=1/5. Thus, in this second example, there isminimal reduction in speed and beam capacity. The coverage area can beincreased as the number of GW's increase. These approaches trade offinitial coverage area and/or speed/capacity for a reduced number ofinitial gateways.

Orbit Slot Independence

Weights vectors, and thus beam locations, are flexible in the satellitecommunications architecture described herein. Change of an orbit slotcan be accomplished by uploading a new set of beam weight vectors toallow coverage of the same areas from a different orbit slot. Thisprovides several benefits. The orbit slot can be undefined at the timethe satellite is being built. The orbit slot can be changed at any timeduring the satellite lifetime. A generic satellite design can be usedfor any orbit slot and any service area definition within the reasonablescan range of the reflector.

Dynamic EIRP Allocation across GW's to Mitigate Rain Fade

In a beamformed Tx system, it is very easy to allocate Tx power to eachGW beam in a non-uniform and dynamic manner. Tx power to a beam isproportional to the sum of the magnitude squared of the beam weights.Scaling the beam weights up or down will increase or decrease the powerto the beam. Power can also be adjusted via the channel amplifierattenuation.

Power can be allocated to each GW beam in inverse proportion to the rainfade attenuation. This allocation can be dynamic based on the actualrain fade attenuation, or static based on the rain fade that isassociated with a particular availability.

In one embodiment, transmit power is allocated to GW's based on downlinkSNR. For N_(GW) Gateways, the total Tx power P_(GW) on the satellitethat is allocated to transmissions to the GW's is

$\begin{matrix}{{\sum\limits_{n = 1}^{N_{GW}}P_{n}} = P_{GW}} & (8)\end{matrix}$

where P_(n)=Tx power allocated to GW number n. The proper powerallocation to equalize downlink SNR is

$\begin{matrix}{P_{n} = {P_{GW} \cdot \frac{L_{n}R_{n}}{D_{n}} \cdot \frac{1}{\sum\limits_{i = 1}^{N_{GW}}\frac{L_{i}R_{i}}{D_{i}}}}} & (9)\end{matrix}$

where R_(n)=satellite antenna gain to GW number n; D_(n)=downlink SNRdegradation due to rain attenuation at GW number n; and L_(n)=free-spacepath loss to GW number n.

In a static approach, power allocations can be selected based on rainattenuation at the target link availability. These fixed powerallocations can be determined by the network planner prior to networkoperation. The rain attenuation, A_(n), can be determined at each GWthat corresponds to the desired availability. The rain degradation,D_(n), can be calculated from A_(n) and the GW HW parameters. Thefree-space path loss, Ln, can be calculated to each GW. The Tx antennagain to each GW, R_(n), can be determined from the beam weights andcomponent beam radiation patterns. The allocated powers, P_(n), and therequired channel amplitude attenuation setting can be calculated toproduce those powers.

The channel amplitude attenuator setting can be sent uplink to thesatellite and kept at that setting until (and if) one desires to changethe network operation concept (e.g., GW locations, downlinkavailability, total power allocated to the GW downlink etc.).

In a dynamic approach, the power allocations can be selected based onthe observed rain attenuation at each GW. The Tx power settings, P_(n),will change dynamically as the rain attenuations changes. In someembodiments, a a rain attenuation measurement system is used, and acentral processing site (e.g., an NOC) to gather all the measured rainattenuations, dynamically compute the power allocations, and send uplinkthe power allocation (e.g., as a channel amplitude gain or a beam weightvector) information to the satellite. FIG. 20 is a simplified diagram ofan illustrative satellite communications system 2000 that can supportthis dynamic approach.

In another embodiment, transmit power is allocated to GW's based onsignal-to-interference-and-noise ratio (SINR). For GW downlinks thathave a lot of “spot beam” interference, it may be better to allocatepower with an objective to equalize downlink SINR.

Both the static approach and the dynamic approach can accommodate thisby using a different equation to calculate the power allocations. Herethe power allocations are

x=[R _(gw) C−λGC(R−R _(gw))]⁻¹ λDg  (10)

where λ is chosen to force the equality

$\begin{matrix}{{\sum\limits_{n = 1}^{N}x_{n}} = P_{GW}} & (11)\end{matrix}$

and the below definitions apply.x: An N×1 column vector, which contains the Tx power allocations to eachGW.R: An N×N beam gain matrix. The component R_(ij) is the gain of the beampointed at GW j in the direction of GW i. The diagonal component r_(ii)is the antenna gain for GW i.R_(gw): An N×N diagonal matrix containing the gain to GW n. The diagonalelements of R_(gw)=the diagonal elements of R.D: An N×N diagonal matrix whose elements contain the rain degradation ofeach GW. This is calculated from the measured values of A_(n).C: An N×N diagonal matrix whose elements contain the link constants ofeach GW. Specifically,

C=Diag[c _(n)]

where

$\begin{matrix}{c_{n} = {\frac{G}{T}{(n) \cdot \frac{1}{L_{p}(n)} \cdot \frac{1 + \alpha}{kW}}}} & (12)\end{matrix}$

G: An N×N diagonal matrix whose diagonal elements contain the targetrelative downlink SINR's for each GW. If it is desired for all GW's tohave the same downlink SINR, then G=the N×N identity matrix.g: An N×1 column vector whose elements are the same as the diagonalelements of G.X: A free scalar parameter that must be chosen such that the powerallocations, x_(n), sum up to the total allocated GW Tx power, P_(GW).Equation (10) can be solved with an iterative technique.

It should be noted that the methods, systems, and devices discussedabove are intended merely to be examples. It must be stressed thatvarious embodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, it should be appreciated that,in alternative embodiments, the methods may be performed in an orderdifferent from that described, and that various steps may be added,omitted, or combined. Also, features described with respect to certainembodiments may be combined in various other embodiments. Differentaspects and elements of the embodiments may be combined in a similarmanner. Also, it should be emphasized that technology evolves and, thus,many of the elements are exemplary in nature and should not beinterpreted to limit the scope of the invention.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, it will be understood by oneof ordinary skill in the art that the embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, algorithms, structures, and techniques have been shownwithout unnecessary detail in order to avoid obscuring the embodiments.

Also, it is noted that the embodiments may be described as a processwhich is depicted as a flow diagram or block diagram. Although each maydescribe the operations as a sequential process, many of the operationscan be performed in parallel or concurrently. In addition, the order ofthe operations may be rearranged. A process may have additional stepsnot included in the figure.

Moreover, as disclosed herein, the term “memory” or “memory unit” mayrepresent one or more devices for storing data, including read-onlymemory (ROM), random access memory (RAM), magnetic RAM, core memory,magnetic disk storage mediums, optical storage mediums, flash memorydevices, or other computer-readable mediums for storing information. Theterm “computer-readable medium” includes, but is not limited to,portable or fixed storage devices, optical storage devices, wirelesschannels, a sim card, other smart cards, and various other mediumscapable of storing, containing, or carrying instructions or data.

Furthermore, embodiments may be implemented by hardware, software,firmware, middleware, microcode, hardware description languages, or anycombination thereof. When implemented in software, firmware, middleware,or microcode, the program code or code segments to perform the necessarytasks may be stored in a computer-readable medium such as a storagemedium. Processors may perform the necessary tasks.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. For example, the above elements may merely be a component ofa larger system, wherein other rules may take precedence over orotherwise modify the application of the invention. In addition, a numberof steps may be undertaken before, during, or after the above elementsare considered. Accordingly, the above description should not be takenas limiting the scope of the invention.

1.-10. (canceled)
 11. A hub-spoke, bent-pipe satellite communicationssystem comprising: a satellite operations controller having a satelliteoperations data output, the satellite operations data specifying a framedefinition comprising a plurality of timeslots for a frame and definingan allocation of capacity between forward traffic and return traffic,the forward traffic being from at least one gateway to a plurality ofterminals, and the return traffic being from the plurality of terminalsto the at least one gateway; and a satellite in communication with thesatellite operations controller and comprising a plurality of bent-pipepathways, such that: during a forward timeslot associated with forwardtraffic according to the frame definition, a pathway is used for forwardtraffic signals; and during a return timeslot associated with returntraffic according to the frame definition, the pathway is used forreturn traffic signals.
 12. The system of claim 11, wherein: during theforward timeslot, additional pathways are used for forward trafficsignals; and during the return timeslot, the additional pathways areused for return traffic signals.
 13. The system of claim 11, wherein thepathway has an uplink of a first polarity and a downlink of a secondpolarity different from the first polarity.
 14. The system of claim 11,wherein one or more of the plurality of bent-pipe pathways comprises aselectable gain amplifier.
 15. The system of claim 14, wherein the gainsetting of one or more of the selectable gain amplifiers is set to aforward timeslot gain setting consistent with a forward channel duringthe forward timeslot and set to a return timeslot gain settingconsistent with a return channel during the return timeslot.
 16. Thesystem of claim 15, wherein the forward timeslot gain setting and thereturn timeslot gain setting are different.
 17. The system of claim 15,wherein two or more of the plurality of selectable gain amplifiers haveindependent gain settings.
 18. The system of claim 11, wherein one ormore of the plurality of bent-pipe pathways comprises a frequencyconverter.
 19. The system of claim 11, wherein one or more of thebent-pipe pathways comprises a filter.
 20. The system of claim 11,wherein the satellite is a geostationary satellite.
 21. A method forhub-spoke, bent-pipe satellite communication utilizing a satellitecontaining a plurality of bent-pipe pathways and in communication with aplurality of terminals and a plurality of gateways, the methodcomprising: determining, according to a frame definition, that a firsttimeslot is a forward timeslot associated with communicating forwardtraffic, and that a second timeslot is a return timeslot associated withcommunicating return traffic, wherein the frame definition defines anallocation of capacity between forward traffic and return traffic ineach of a plurality of timeslots for a frame, the forward traffic beingfrom at least one gateway to a plurality of terminals, and the returntraffic being from the plurality of terminals to the at least onegateway; using a pathway for forward traffic signals during the forwardtimeslot; and using the pathway for return traffic signals during thereturn timeslot.
 22. The method of claim 21, wherein: during the forwardtimeslot, additional pathways are used for forward traffic signals; andduring the return timeslot, the additional pathways are used for returntraffic signals.
 23. The method of claim 21, wherein: the pathway has anuplink of one polarity and a downlink of a different polarity.
 24. Themethod of claim 21, further comprising: selectively amplifying a forwardor return traffic signal by one or more of the plurality of bent-pipepathways.
 25. The method of claim 24, further comprising, by one or moreof the plurality of bent-pipe pathways: amplifying with a forwardtimeslot gain setting consistent with a forward channel during theforward timeslot; and amplifying with a return timeslot gain settingconsistent with a return channel during the return timeslot.
 26. Themethod of claim 25, wherein the forward timeslot gain setting and thereturn timeslot gain setting are different.
 27. The method of claim 24,further comprising: amplifying with independent gain settings at two ormore of the plurality of pathways.
 28. The method of claim 21, furthercomprising: frequency converting a signal at one or more of theplurality of bent-pipe pathways.
 29. The method of claim 21, furthercomprising: filtering a signal at one or more of the plurality ofbent-pipe pathways.
 30. A hub-spoke, bent-pipe satellite communicationssystem comprising: means for determining, according to a framedefinition, that a first timeslot is a forward timeslot associated withcommunicating forward traffic, and that a second timeslot is a returntimeslot associated with communicating return traffic, wherein the framedefinition defines an allocation of capacity between forward traffic andreturn traffic in each of a plurality of timeslots for a frame, theforward traffic being from at least one gateway to a plurality ofterminals, and the return traffic being from the plurality of terminalsto the at least one gateway; means for using a bent-pipe pathway of asatellite for forward traffic signals during the forward timeslot; andmeans for using the pathway for return traffic signals during the returntimeslot.
 31. The system of claim 30, further comprising: means forselectively amplifying a forward or return traffic signal by thepathway.
 32. The system of claim 31, further comprising: means foramplifying, in the pathway, with a forward timeslot gain settingconsistent with a forward channel during the forward timeslot; and meansfor amplifying, in the pathway, with a return timeslot gain settingconsistent with a return channel during the return timeslot.
 33. Thesystem of claim 31, wherein the pathway is one of a plurality ofbent-pipe pathways of the satellite, and further comprising: means foramplifying with independent gain settings at two or more of theplurality of pathways.
 34. The system of claim 30, further comprising:means for frequency converting a signal at the pathway.
 35. The systemof claim 30, further comprising: means for filtering a signal at thepathway.